.  .    LIBRARY    .  . 

Connecticut 
Agricultural  College. 

VOL J...0..O  ..S.  5 _._Z 

CLASS   NO .5...5...Q. 

C  OST S...^^. 

DATE .^.iM,s4L..(e. 19a.A.. 


DEPARTMENT    OF   THE    INTEUIOR 


MONOGRAPHS 


OF  THE 


United  States  Geological  Survey 


VOLUME    XLYI 


WASHINGTON 

GOVERNMENT     PRINTING     OFFICE 
1904 


Digitized  by  the  Internet  Archive 

in  2009  with  funding  from 

Boston  Library  Consortium  IVIember  Libraries 


http://www.archive.org/details/menomineeironbeaOObayl 


UNITED    STATES    GEOLOGICAL    SURVEY 

CHARLES   D.  WALCOTT,  DIRECTOR 


THE 


MENOMINEE  IRON-BEARING  DISTRICT  OF  MICHIGAN 


BY 


WILLIAM   SHIRLEY  BAYLEY 


CHARLES    RICHARD    VAN    HISE,  Geologist   in    Charge 


WASHINGTON 

GOVERNMENT     PRINTING     OFFICE 
1904 


0  O  8  5 


CONTEJ^TS, 


Page. 

Letter  of  Transmittal 17 

Outline  op  Monograph '..S 19 

Chapter  I. — Introduction 33 

Scope  and  date  of  work  done 33 

Acknowledgments 33 

Limits  of  the  Menominee  area 34 

Relations  to  other  iron-bearing  areas 34 

Shape  and  size  of  the  Menominee  tongue 35 

Economic  importance  of  the  district 35 

Previous  work  in  the  district - 36 

Method  of  work 37 

Classification  of  formations 38 

Names  of  the  formations 39 

References  to  Marquette  monograj)h 40 

Chapter  II. — Bibliography  and  Abstract  of  Liter.\ture 41 

Chapter  HI. — Physiography 125 

Topography 125 

Drainage 126 

Origin  of  the  topography 127 

Pre-Cambrian  topography 129 

Chapter  IV. — The  Archean  System 1.30 

Section  1 .  Quinnesec  schists 131 

Relations  to  overlying  formations 131 

The  southern  area 131 

Distribution 131 

Topography 132 

Composition  and  structure  of  the  rock  series 133 

Lithology 134 

Greenstone-schists  and  associated  greenstones 135 

Coarse-grained  varieties 136 

Gabbros  and  their  derived  schists 136 

Diabases  and  their  derived  schists ., 1.39 

Diorites  and  their  derived  schists 139 

Fine-grained  varieties 141 

Origin  of  the  schistosity 142 

Basic  lavas  and  their  derived  schists 142 

Basic  tufts  and  their  derived  schists 144 

Chlorite-schists 145 

Amphibolites 146 

5 


6  CONTENTS. 

Chapter  IV. — The  Archean  System — Continued.  Page. 
Section  1.  Quinnesec  schists — Continued. 
The  southern  area — Continued. 
Lithology — Continued. 

Origin  of  the  basic  schists .; 148 

Acid  intrusives  and  their  derived  schists 149 

Gneissoid  granite  and  granite-gneisses 150 

Porphyries  and  felsites  and  their  schistose  phases 153 

Sericite-schists 154 

Interesting  localities 155 

Sturgeon  Falls 155 

Little  Quinnesec  Falls 156 

Big  Quinnesec  Falls 157 

Horserace  Rapids 158 

The  western  area 159 

Distribution 159 

Topography 159 

Lithology 160 

Fine-grained  greenstones  and  their  derived  schists 162 

Coarse-grained  greenstones  and  their  derived  schists 163 

Fragmental  schisfe 164 

Origin  of  the  rocks 165 

Interesting  localities 165 

Upper  Twin  Falls 166 

Lower  Twin  Falls 166 

Fourfoot  Falls 166 

Section  2.  Northern  Complex 167 

Distribution 168 

Topography 168 

Sequence  of  rocks 168 

Lithology .■ 169 

Gneissoid  granites 169 

Banded  gneisses 1 70 

Hornblende-schists 171 

Intrusives 172 

Acid  intrusives 172 

Basic  intrusives 173 

Interesting  localities 174 

Ch.^pter  V. — The  Algonkian  System 175 

General  character  and  definition 175 

Unconformity  within  the  system 175 

Section  1 .  Lower  Menominee  series 176 

Succession  and  distribution 1 76 

Sturgeon  quartzite 177 

Distribution  and  topography 177 

Lithology 179 

Conglomerates 179 

Arkoses  and  gray wackes 181 

Quartzite '- 183 

Dolomitic  quartzite 185 

Veins  and  dikes  in  the  quartzite 185 


CONTENTS.  7 

Chapter  V. — The  Algonkian  System — Continued.  Page. 
Section  1.  Lower  Menominee  series — Continued. 
Sturgeon  quartzite — Continued. 

Folding 186 

Thicliness 187 

Relations  to  underlying  formations 188 

Interesting  localities 189 

The  "rock  dam"  on  Pine  Creek 189 

Black  Creek 194 

North  half  of  sec.  7,  T.  39  N.,  R.  28  W 195 

West  half  of  sec.  8,  T.  39  N.,  R.  28  W 196 

Falls  of  the  Sturgeon 196 

Randville  dolomite 200 

Distribution  and  topography 200 

The  northern  belt 200 

The  central  belt 201 

The  southern  belt 203 

Distribution 203 

Topography 208 

Lithology  209 

Dolomite  and  dolomitic  sandstone 210 

Dolomite  breccias  and  conglomerates 215 

Talpose  schists 221 

Argillaceous  rocks 225 

Cherty  quartz  rocks 226 

Conclusions  from  microscopical  study,  and  comparison  with  similar 

rocks  in  the  Marquette  and  Gogebic  districts 229 

Origin  of  the  dolomites  and  cherty  quartz  rocks 230 

Folding 232 

Major  folding 232 

Cross  folding 233 

Minor  folding 235 

The  northern  belt _ 235 

The  central  belt 235 

The  southern  belt 237 

Marginal  folds : 237 

Walpole  fold 238 

Pewabic  fold  239 

Quinnesec  fold 239 

Norway  fold 240 

Aragon  fold 242 

West  Vulcan  fold 245 

Other  secondary  folds  at  southern  margin 246  - 

Secondary  folds  at  northern  margin 246 

Interior  folds 247 

Thickness 248 

Relations  to  adjacent  formations 250 

Relations  to  underlying  Sturgeon  quartzite 250 

Relations  to  overlying  Negaunee  formation 251 

Relations  to  basal  member  of  the  Upper  Huronian 252 

Relations  to  other  formations 254 


8  CONTENTS. 

Chapter  V. — The  Algonkian  System — Continued.  Page 
Section  1.  Lower  Menominee  series — Continued. 
Randville  dolomite — Continued. 

Interesting  localities 255 

In  the  northern  belt  255 

Northeast  quarter  of  sec.  3,  T.  40  N. ,  R.  30  W 2.55 

Northeast  quarter  of  sec.  14,  T.  40  N. ,  R.  30  W 255 

In  the  central  belt 256 

Southwest  quarter  of  sec.  22,  T.  40  N.,  R.  30  W 256 

Iron  Hill 2.56 

In  the  southern  belt 260 

Southeast  side  of  Lake  Antoine 260 

Southeast  quarter  of  sec.  32,  and  southwest  quarter  of  sec. 

33,  T.  40  N.,  R.  30  W 261 

North  and  northeast  of  Quinnssec 263 

Northwest  quarter  of  sec.  9,  T.  .39  N. ,  R.  29  W 267 

Sees.  12  and  13,  T.  39  N.,  R.  29  W 271 

Negaunee  formation 273 

Distribution 274 

Lithology 275 

Relations  to  adjacent  formations 277 

Conclusions  from  foregoing  study 277 

Section  2.  Upper  Menominee  series 280 

Character  and  occurrence 280 

Component  formations 280 

Separation  from  the  overlying  sandstones  and  the  underlying  Lower  Menomi- 
nee series 280 

Distribution 283 

Folding 284 

Vulcan  formation 285 

Distribution 285 

Topography 291 

Subdivision  into  members 291 

Traders  member 291 

Distribution 291 

Lithology 294 

Slates 295 

Macroscopical 295 

Microscopical  and  chemical 297 

'             Conglomerates  and  quartzites 300 

Macroscopical 300 

Microscopical 302 

Jaspilites 307 

Macroscopical 307 

Microscopical _ 313 

Brier  slate 320 

Distribution 320 

Lithology 324 

Macroscopical 324 

Microscopical  and  chemical 326 


CONTENTS.  9 

Chapter  V. — The  Algonkian  System — Continued.  Page. 
Section  2.  Ujjper  Menominee  series — Continued. 
Vulcan  formation — Contiimed. 

Subdivision  into  members — Continued. 

Curry  member 331 

Distribution 331 

Lithology  333 

Macroscopical 333 

Microscopical 339 

Eelations  between  the  members  of  the  Vulcan  formation 349 

Genesis  352 

Folding 356 

Folds  of  lower  orders 356 

Folds  of  higher  orders 356 

Secondary  structures  resulting  from  folding 358 

Thickness 359 

Relations  between  the  Vulcan  and  adjacent  formations 36] 

Explanation  of  the  distribution  and  relations  of  the  Vulcan  and  Hanbury  forma- 
tions to  the  underlying  formations 37O 

The  ores  373 

Lithology  373 

Physical  characters 373 

Chemical  composition 378 

Mineralogical  composition 384 

Mineral  constituents  of  the  ores 384 

Minerals  associated  with  the  ores  386 

Quartz,  dolomite,  and  calcite 386 

Pyrite  and  chalcopyrite 388 

Other  minerals  in  joint  cracks 388 

Serpentine 389 

Talc 390 

Efflorescence  on  ores 390 

The  ore  deposits 399 

Distribution  and  shapes 399 

Development  of  the  deposits 395 

Topographic  relations  of  the  deposits 401 

Time  and  depth  of  concentration 403 

Illustrations  of  deposits,  including  geology  of  the  important  mines 404 

Loretto-Appleton  deposit 4O4 

Traders-Forest  belt 407 

Traders  mine 407 

Cornell  mine 410 

Cuff  mine 410 

Indiana  mine 4j  1 

Forest  mine 412 

The  southern  belt 413 

Chapin-Pewabic  deposits 414 

Walpole  mine 414 

Pewabic  mine 418 

Chapin  mine 420 


10  CONTENTS. 

Chapter  V. — The  Algonkian  System — Continued.  Page. 
Section  2.  Upper  Menominee  series — Continued. 
The  ores — Continued. 

The  ore  deposits — Continued. 

Illustrations  of  deposits,  etc. — Continued. 
The  southern  belt — Continued. 

Old  Keel  Ridge  mine 423 

Keel  Ridge  mine 424 

Quinnesec,  Cundy,  and  Vivian  mines 425 

Norway  and  Cyclops  mines 428 

Aragon  mine 432 

Mines  east  of  Aragon  mine 434 

Brier  Hill  and  Curry  mines 434 

West  Vulcan  mine 439 

Central  Vulcan  area 449 

East  Vulcan  mine 450 

Verona  mine 453 

Emmett  and  Breen  mines 453 

Summary 455 

Other  localities  of  the  Vulcan  formation 456 

Sees.  25  and  26,  T.  40  N.,  R.  31  W 456 

Sec.  33,  T.  40N.,  R.  30  W 457 

Sees.  1  and  2,  T.  39  N.,  R.  30  W 458 

Sec.  6,  T.  39  N.,  R.  29  W 459 

Sees.  12andl3,  T.  39N.,  R.  29  W 461 

Hanbury  slate 462 

Distribution  and  topography 462 

Lithology 462 

Clay  slates 463 

Gray wackes  and  quartzites 464 

Calcareous  slates  and  dolomites 466 

Cherts  and  ferruginous  oxides 467 

Igneous  rocks  and  their  contact  deposits 468 

Folding  and  secondary  structures 469 

Thickness 470 

Relations  to  Paleozoic  beds 471 

Interesting  localities 471 

Typical  localities 471 

Sec.  13,  T.  40  N.,  R.  31  W 471 

Hanbury  Hill 472 

Sturgeon  Mills 475 

Sees.  29  and  30,  T.  39  N,  R.  28  W 476 

Localities  at  which  cherts  occur 476 

Sec.  15,  T.  40N.,  R.  30  W 476 

Sec.  11,  T.  39  N.,  R.  30  W 477 

Southeast  quarter  of  sec.  7  and  southwest  quarter  of  sec.  8,  T.  39 

N.,R.  29W 478 

Iron  Hill,  southeast  quarter  of  sec.  32,  T.  40  N.,  R.  29  AV 481 

Sec.  17,  T.  39  N.,  R.  29  W 483 


CONTENTS.  11 

Chapter  V. — The  Algonkian  System — Continued.  Page. 
Section  2.  Upper  Menominee  series — Continued. 
Hanbury  slate — Continued. 

Interesting  localities — Continued. 

Localities  at  which  cherts  occur — Continued. 

Northwestquarterof  sec.  26,  T.  39N.,  R.  29  W 484 

Sec.  21,  T.  39N.,  R.  28  W 484 

Sec.  19,  T.  39  N.,  R.  28  W 484 

Possible  iron-ore  deposits 486 

Chapter  VI. — The  Paleozoic  Sy.stem 489 

Section  1 .  Lake  Superior  sandstone 489 

Character  and  relations 489 

Age 493 

Section  2.  Hermansville  limestone 494 

Chapter  VII. — Outline  op  Geological  History 495 

Resum^  of  formations 495 

Succession  of  events 495 

Archean 495 

Lower  Menominee  deposition 496 

Inter-Menominee  unconformity 497 

Upper  Menominee  deposition 497 

Folding  and  metamorphism 498 

Post-Huronian  unconformity 499 

Paleozoic  deposition 500 

Post- Paleozoic  history 500 

Correlation  with  other  iron-bearing  districts  of  the  Lake  Superior  region 501 

Index 503 


ILLUSTRATIONS. 


Page. 
Plate  I.  Geological  map  of  part  of  the  Lake  Superior  region,  showing  relative  position  of  the 

Menominee  with  respect  to  other  Huronian  areas 33 

II.  General  outline  map  of  the  region  between  the  Menominee  River  and  the  north  side 
of  the  Felch  Mountain  district,  showing  position  of  the  Menominee  trough  with 
respect  to  other  Huronian  troughs  to  the  north 34 

III.  Portion  of  the  geological  map  of  the  ilenominee  iron  region,  by  T.  B.  Brooks,  1872  ..         60 

IV.  Portion  of  the  geological  map  of  the  Menominee  iron  region,  Ijy  T.  B.  Brooks  and  C. 

E.  Wright,  1879 66 

V.  Outline  geological  map  of  the  Menominee  iron  region,  by  R.  D.  Irving,  1890 9-1 

VI.  Organic  markings  in  the  Lake  Superior  iron  ores.     From  a  photograph.     After  W.  S. 

Gresley 118 

VII.  Organic  markings  in  the  Lake  Suiierior  iron  ores.     From  a  photograph.     After  W.  S. 

Gresley 120 

VIII.  Topographical  map  of  the  Menominee  iron  district In  pocket. 

IX.  Geological  map  and  sections  of  the  Menominee  iron  district In  pocket. 

X.  A,  View  from  brink  of  Sturgeon  Falls,  looking  down  stream;  B,  Menominee  River 

above  Sturgeon  Falls 132 

XI.  A,  Horserace  Rapids  during  high  water;  £,  Log  jam  in  Horserace  Rapids 158 

XII.  A,  Basin  below  Vpper  Twin  Falls;  B,  Barrier  rock  at  Upper  Twin  Falls 160 

XIII.  A,  Brecciated  band  of  fine-grained  greenstone  at   Upper  Twin  Falls;   B,  Ridge  of 

dolomite,  south  of  Lake  Antoine 162 

XIV.  Sketch  map  of  exposures  near  the  contact  between  the  Sturgeon  quartzite  and  the 

Archean  complex,  in  T.  40  N.,  R.  30  W.,  and  T.  41  N.,  R.  29  W 186 

XV.  .1,  View  of  dolomite  bluffs  on  north  side  of  highway  between  Quinnesec  and  Norway; 

B,  Nearer  view  of  bluff  shown  in  .1 208 

XVI.  A,  Brecciated  Rand  villa  dolomite  on  wall  at  east  end  of  gorge,  east  of  Aragon  mine; 

B,  Dolomite  conglomerate  at  Iron  Hill 218 

XVII.  A,  Fold  in  chert  at  Iron  Hill;  B,  Folds  in  Traders  jaspilite,  we.st  side  of  Clifford  pit. 

Traders  mine 234 

XVIII.  Maps   showing   magnetic   observations   over   strips   of    country   bordering  areas   of 

Quinnesec  schists  and  Randville  dolomite 286 

XIX.  Photomicrographs  of  rocks  of  the  Vulcan  formation 316 

XX.  Folds  in  jaspilites  in  the  Vulcan  formation 356 

XXI.  A,  Brecciated  Brier  slates  in  Norway  pit;  B,  Band  of  brecciated  Brier  slate  crossing 

definitely  bedded  slates  transversely  to  their  bedding,  in  Norway  pit 364 

XXII.  A,  Surface  of  ore  breccia  near  contact  of  the  Traders  member  with  the  Brier  slates, 

No.  3  pit,  Curry  mine;  B,  Concentrating  works  at  Pewabic  pit 368 

XXIII.  Hypothetical  geological  map  of  the  Loretto  and  Appleton  areas , 404 

XXIV.  Geological  map  of  Traders  and  Cornell  mines  and  vicinity 406 

13  . 


14  ILLUSTRATIONS. 

Page. 

Plate  XXV.  Geological  map  of  the  country  adjacent  to  the  Cuff  and  Indiana  mines 410 

XXVI.  ,1,  View  east  from  D  shaft,  Chapin  mine,  showing  shafts  on  Walpole-Chapin 
fold;  B,  View  west  from  A  shaft,  Chapin  mine,  showing  distribution  of  shafts 

on  Chapin  property 416 

XXVII.  Outlines  of  ore  bodies  on  fifth,  sixth,  seventh,  and  tenth  levels,  Chapin  mine, 

showing  dip  and  pitch  of  ore  bodies 420 

XXVIII.  Geological  map  of  the  Chapin-Pewabic  folds 422 

XXIX.  Geological  map  and  section,  southeast  quarter  of  sec.  32,  T.  40  N.,  P.  30  W.,  and 

portion  of  adjacent  sec.  33 424 

XXX.  Geological  map  and  sections  of  the  Quinnesec  area 426 

XXXI.  Geological  map  of  the  Norway  and  Aragon  folds 428 

XXXII.  Vertical  cross  sections  through  the  Norway  and  Aragon  folds,  illustrating  geo- 
logical structure i 430 

XXXIII.  Geological  map  of  north  half  of  sec.  9,  T.  39  N.,  P.  29  W.,  including  the  Aragon 

West  Vulcan,  Prier  Hill,  and  Curry  mines 434 

XXXIV.  Geological  map  of  Central  Vulcan  and  portion  of  West  Vulcan  areas 438 

XXXV.  Geological  majj  of  East  Vulcan  and  Verona  areas 450 

XXXVI.  Geological  map  of  the  Emmett  and  Breen  mines  and  vicinity,  Waucedah 4.52 

XXXVII.  Geological  map  of  portions  of  sees.  25,  26,  35,  and  36,  T.  40  N.,  P.  31  W 454 

XXXVIII.  Geological  map  of  soiith  half  of  sec.  33,  T.  40  N.,  P.  30  W 456 

XXXIX.  Geological  map  of  portions  of  sees.  1  and  2,  T.  39  N.,  P.  30  W.,  and  sees.  35  and 

36,  T.  40  N.,  P.  30  W 458 

XL.  Geological  map  of  southeast  portion  of  sec.  6,  T.  39  N. ,  P.  29  W 460 

XLI.  Geological  map  of  portions  of  sees.  12  and  13,  T.  39  N.,  P.  29  W 462 

XLII.  Map  of  exposures  at  Iron  Hill  in  sec.  32  and  neighboring  portion  of  sec.  33,  T.  40 

N.,P.  29W 480 

XLIII.  View  of  unconformity  between  the  Traders  jaspilites  and  the  Lake  Superior 

sandstone,  west  side  Quinnesec  open  pit 492 

Jig.    1.  Geological  section  across  the  Menominee  district  from  Little  Bekuenesec  Falls  north- 
ward.    After  Foster  and  Whitney,  1851 46 

2.  Portion  of  the  geological  map   of   the  Lake  Superior  land  district  in  the  State  of 

Michigan.     After  Foster  and  Whitney,  1851 48 

3.  Geological  section  along  the  Falls  of  the  Sturgeon  Piver.     After  H.  Credner,  1869 51 

4.  Geological  section  across  the  Menominee  district.     After  H.  Credner,  1869 '..  52 

5.  Portion  of  geological  map  of  the  Upper  Peninsula  of  Michigan.     After  H.  Credner, 

1869 54 

6.  Geological  section  through  Sturgeon  Falls.     After  T.  B.  Brooks,  1873 58 

7.  Geological  section  through  Lake  Antoine.     After  T.  B.  Brooks,  1873 59 

8.  Geological  section  through  Quinnesec.     After  T.  B.  Brooks,  1880 68 

9.  Geological  section  through  Sturgeon  River.     After  T.  B.  Brooks,  1880 68 

10.  Structure  section  across  the  Menominee  region  through  the  west  end  of  Lake  Fumee. 

After  T.  B.  Brooks,  1880 69 

11.  Structure  section  across  the  Menominee  district  in  the  vicinity  of  Twin  Falls.     After 

T.  B.  Brooks,  1880 69 

12.  Hypothetical  section  through  the  Menominee  region  in  the  vicinity  of  Quinnesec  Val- 

ley.    After  P.  D.  Irving,  1890 93 

13.  Sketch  map  of  exposures  in  north  half  of  sec.  32,  T.  41  N.,  P.  29  W.,  showing  relation 

between  conglomerates  and  gneisses 192 


ILLUSTRATIONS.  15 

Page. 
Fio.  14.  Sketch   map  of  exposures  on   Black   Creek,  showing  relation  of  conglomerates  to 

gneisses 194 

15.  Sketch  map  of  exposures  at  and  near  the  Falls  of  the  Sturgeon  River 195 

16.  Cross  section  through  pits  and  shafts  near  the  center  of  sec.  25,  T.  40  N.,  R.  31  W 204 

17.  Sketch  plan  of  Cuff  mine  and  vicinity 236 

18.  Vertical  north-south  cross  section  of  the  Norway  and  Aragon  mines 242 

19.  Longitudinal  section  through  the  Norway  pit 243 

20.  Horizontal  section  of  the  Aragon  mine  at  the  fifth  level 243 

21.  Horizontal  section  of  the  Aragon  mine  at  the  sixth  level 244 

22.  Sketch  map  of  exposures  near  Sturgeon  Falls,  sec.  26,  T.  39  N. ,  R.  29  W 288 

23.  Sketch  of  contortions  in  jasper  bands,  west  side  of  Clifford  pit,  illustrating  production 

of  breccias 302 

24.  Diagrammatic  sketch  illustrating  folding  in  the  iron  formation  on  east  side  of  pit  at 

old  Keel  Ridge  mine 357 

25.  Sketch  illustrating  puckering  in  jaspilite  on  stripped  surface,  west  end  of  Clifford  pit. 

Traders  mine,  1899 358 

26.  Sketch  illustrating  folding  in  Brier  slates  on  wall  of  trench  from  No.  2  pit,  "West  Vul- 

can mine 358 

27.  Sketch  illustrating  puckering  in  Brier  slates,  west  side  of  cut  at  Curry  shaft  No.  1 358 

28.  Calcite  crystal  in  ore  of  ^V'est  Vulcan  mine 387 

29.  Calcite  crystal  in  ore  of  West  Vulcan  mine 387 

30.  Vertical  north-south  cross  section  of  the  Loretto  mir  e 405 

31.  Horizontal  section  of  the  Loretto  mine  at  the  first  level 405 

32.  Vertical  east-west  longitudinal  section  of  the  Loretto  mine 406 

33.  Sketch  map  of  exposures  in  south  half  of  sec.  25,  T.  40  N.,  R.  30  W 413 

34.  Horizontal  section  of  the  Walpole  mine  at  the  third  level  417 

35.  Horizontal  section  of  the  Pewabic  mine  at  the  third  level 418 

36.  Vertical  section  through  No.  1  shaft  along  north-south  crosscut,  first  level,  Pewabic 

mine 419 

37.  Vertical  north-south  cross  section  through  shaft  D,  Chapin  mine 421 

38.  Vertical  north-south  cross  section  through  No.  2  and  C^  shafts,  Chapin  mine 422 

39.  Horizontal  section  of  the  Aragon  mine  at  the  first  level 432 

40.  Horizontal  section  of  the  Aragon  mine  at  the  eighth  level 433 

41.  Vertical  east-west  longitudinal  section  of  the  Aragon  mine,  north  fold 434 

42.  Section  across  Vulcan  formation  about  600  feet  west  of  Brier  Hill  mine 435 

43.  Plan  of  No.  3  pit,  Curry  mine,  and  section  along  its  north  end 438 

44.  Horizontal  section  of  the  West  Vulcan  mine  at  the  eighth  level 441 

45.  Vertical  north-south  cross  section  through  No.  2  shaft.  West  Vulcan  mine 442 

46.  Vertical  north-south  cross  section  through  Burnt  shaft.  West  Vulcan  mine 443 

47.  Horizontal  section  of  the  West  V^ulcan  mine  at  the  twelfth  level 444 

48.  Horizontal  section  of  the  AVest  Vulcan  mine  at  the  thirteenth  level 445 

49.  Vertical  north-south  cross  section  through  the  V/est  Vulcan  mine  2.50  feet  east  of  the 

Burnt  shaft 446 

50.  Horizontal  section  of  the  West  Vulcan  mine  at  the  fifteenth  level , 447 

51.  Horizontal  section  of  the  East  Vulcan  mine  at  the  eighth  level.  No.  4  shaft 450 

52.  Vertical  north-south  cross  section  through  shaft  No.  3,  East  Vulcan  mine 451 

53.  Vertical  north-south  cross  section  through  shaft  No.  4,  East  Vulcan  mine 452 

54.  Sketch  map  of  explorations  at  Turner's  location,  sec.  19,  T.  39  N. ,  R.  28  W 485 


LETTER  OF  TRAI^SMITTAL. 


Department  of  the  Interior, 
United  States  Geological  Survey, 
,  Madison,  Wis.,  April  20,  1903. 

Sir:  I  have  the  honor  to  transmit  herewith  the  manuscript  of  a 
monograph  on  the  Menominee  Iron-bearing  District  of  Michigan,  by 
William  Shirley  Bayley.  This  monograph  is  the  sixth  and  last  one  of  a 
series  treating  of  the  iron-bearing  districts  of  the  Lake  Superior  region. 
Monographs  on  the  Penokee-Gogebic,  Marquette,  Crystal  Falls,  Mesabi, 
and  Vermilion  districts  have  already  been  published.     (See  PI.  I.) 

The  first  monograph  on  the  Lake  Superior  region  to  be  published  by 
the  United  States  Geological  Survey  was  that  on  the  copper-bearing  rocks, 
by  Prof  R.  D.  Irving.  The  completion  of  the  original  plans  of  the  old 
Lake  Superior  Division  will  be  marked  by  the  publication  of  a  closing- 
monograph  on  the  general  geology  of  the  Lake  Superior  region. 
Very  respectfully, 

C.  R.  A^AN    HiSE, 

Geologist  in  Charge. 
Hon.  Charles  D.  AValcott, 

Director  of  United  States  Geological  Survey. 

MON  XLVI — 04 -2  17 


OUTLINE  OF  MONOGRAPH. 


Chapter  I.  The  Menominee  district  is  situated  on  the  Michigan  side  of  the 
Menominee  River.  It  occupies  an  area  of  112  square  miles,  lying  principallj'  in 
townships  39  and  -±0  north  and  ranges  28,  29,  30,  and  31  west.  It  consists  of  a 
narrow  tongue,  widening  to  the  west  into  the  broad  expanse  of  the  Crj^stal  Falls 
district,  and  merging  to  the  northwest  into  the  southwestern  end  of  another  ore- 
bearing  district  'known  as  the  Calumet  area.  The  importance  of  the  Menominee 
district  as  an  ore  producer  ma}'  be  inferred  from  the  fact  that  since  the  first  regular 
shipments  of  ore  were  made  in  1S77  the  total  quantity  of  ore  raised  from  its 
mines  has  aggregated  about  29,000,000  tons,  nearly  all  of  which  was  of  Bessemer 
grade.     The  gross  product  in  1902  was  over  3,000,000  tons. 

The  rocks  of  the  district  belong  to  the  Archean,  the  Algonkian,  and  the  Paleozoic 
systems.  The  iron-bearing  beds  are  Algonkian.  These  are  bounded  on  the  north 
by  a  complex  of  gneisses  and  schists  and  on  the  south  by  a  series  composed  mainly 
of  greenstone-schists  cut  by  dikes  of  granite,  porphyry,  gabbro,  and  diabase.  The 
Algonkian  rocks  are  divided  into  a  lower  and  an  upper  series,  distinguished  as  the 
Lower  Menominee  and  the  Upper  Menominee,  separated  by  an  unconformity.  These 
correspond  to  the  Lower  Marquette  and  the  Upper  Marquette  series  in  the  Marquette 
district  and  to  the  Lower  Huronian  and  the  Upper  Huronian  on  the  north  shore  of 
Lake  Huron.  The  Paleozoic  rocks  are  represented  by  the  Lake  Superior  sandstone 
and  an  Ordovician  limestone. 

Chapter  II.  An  abstract  of  the  literature  devoted  to  the  discussion  of  the 
geology  of  the  district  is  given  in  this  chapter.  It  begins  with  a  reference  to  a 
report  by  George  N.  Sanders,  printed  in  1845,  and  ends  with  a  reference  to  a 
general  article  on  the  iron-ore  deposits  of  the  Lake  Superior  region  by  C.  R.  Van 
Hise,  which  was  issued  in  1901. 

Chapter  III.  This  chapter  treats  of  the  physiographj^  of  the  district.  The 
topography  is  simple.  It  consists  essentially  of  two  longitudinal  ridges,  with  eleva- 
tions of  about  1,500  feet,  separated  by  valleys,  the  floors  of  which  are  about  1,000 
feet  above  the  sea.  Both  the  tops  of  the  ridges  and  the  floors  of  the  valleys  slope 
gradually  to  the  southeast,  representing,  it  is  believed,  two  plains.  The  ridges  are 
thus  remnants  of  a  higher  plain  that  once  occupied  the  entire  area  under  discussion. 
The  plan  of  the  topography  corresponds  closely  with  the  geological  structure  of  the 
district.     The  residuals  of  the  high  plain  are  composed  of  hard  dolomites,  while  the 

vallevs  are  carved  in  soft  slates. 

19 


20  OUTLINE  OF  MONOGRAPH. 

The  drainage  is  mainly  lonoitudinal.  The  main  di-ainage  course  is  the  Menom- 
inee River.  The  smaller  streams  are  branches  of  this.  All  the  streams  possess  the 
characteristic  features  of  antecedent  streams.  Their  courses  are  arranged  without 
regard  to  the  geology.  It  is  evident  that  the  present  topography  could  not  have 
been  produced  by  the  present  drainage.  It  not  only  antedates  the  Glacial  epoch, 
at  the  close  of  which  the  present  drainage  was  inaugurated,  but  it  even  antedates 
in  great  measure  the  latest  epoch  of  the  Cambrian  period,  during  which  the  Lake 
Superior  sandstone  was  deposited.  During  this  time  the  entire  district  was  under 
water  and  the  sand  deposit  covered  all  the  hills  as  well  as  filled  all  the  valleys  that 
had  been  made  prior  to  this  period.  Later,  the  land  was  raised  above  the  water 
surface  and  erosion  swept  away  the  sandstone,  except  that  on  the  tops  of  the  hills, 
and  the  old  topography  was  again  brought  to  view.  The  present  topography  of 
the  district  is  therefore  similar  to  that  which  existed  prior  to  Upper  Cambrian  time. 
Chaptek  IV.  The  Archean  crystallines  bordering  the  Algonkian  tongue  are 
greenstone-schists  on  the  south  and  a  complex  of  gneisses,  granites,  and  various 
schists  on  the  north.  The  southern  schists — the  Quinnesec  schists — occur  in  two 
areas.  A  southern  area  lies  along  the  Menominee  River  and  stretches  southward 
into  Wisconsin.  A  western  area  constitutes  a  wedge  entering  the  Huronian  Ijeds 
from  the  west  and  extending  for  6  or  7  miles  along  the  middle  line  of  the  Menom- 
inee tongue.  The  Quinnesec  schists  of  the  southern  area  are  coarse-  and  fine-grained 
basic  rocks,  characterized  by  a  schistose  structure  of  varying  degrees  of  perfection. 
The  coarser  phases  were  originallj-  gabbros,  diabases,  and  diorites;  the  finer  phases 
were  basalts,  diabases,  and  basic  tuffs.  Associated  with  these  are  chlorite-schists, 
amphibolites,  gneisses,  schistose  porphyries,  schistose  felsites,  and  sericite-schists. 
The  acid  schists,  except  perhaps  the  sericite-schists,  are  apophyses  from  a  great  boss 
of  granite  which  is  intruded  in  the  basic  rocks  south  of  the  Menominee  River.  The 
basic  schists  are  cut  by  dikes  of  various  basic  rocks  and  bj-  granites. 

In  the  western  area  the  rocks  are  more  massive.  They  are  dense,  grayish  green 
in  color,  and  uniform  in  their  features.  Some  of  them  are  ellipsoidal.  All  are 
apparently  fine-grained  basic  lavas  that  have  suffered  extreme  alteration.  Most  of 
the  rocks  are  schistose,  some  slightl^y  so  but  others  markedly  so.  Their  schistosity, 
as  well  as  that  of  the  southern  schists,  is  ascribed  to  pressure. 

The  northern  complex  of  gneisses  and  schists  is  of  the  usual  character  of 
Archean  complexes.  Banded  gneisses  and  gneissoid  granites,  hornblende-schists, 
greenstone-schists,  and  a  few  mica-schists  are  intruded  by  dikes  of  diabase  and  by 
veins  and  dikes  of  granite.  The  gneissoid  granites  are  of  a  pink  and  a  graj'  variety, 
of  which  the  former  appears  to  partake  largely  of  the  nature  of  pegmatite.  It 
intrudes  the  gray  variety  in  irregular  stringers  and  in  series  of  narrow  parallel  veins. 

When  in  the  form  last  named,  the  two  rocks  together  give  rise  to  banded 
gneisses.  A  few  localities  are  described  at  which  the  Quinnesec  schists  and  the 
northern  complex  can  be  seen  in  good  exposures. 

Chapter  V.  The  Algonkian  rocks  comprising  the  Menominee  tongue  are  almost 
exclusively  sedimentary,  and  are  mainly  mechanical  sediments.     They  are  separated 


OUTLINE  OF  MONOGRAPH.  21 

from  the  underlyiug  granites  and  gneisses  of  the  northern  complex  by  conglomerates 
composed  largely  of  the  debris  of  the  underlying  rocks.  Their  relations  with  the 
Quinnesec  schists  are  not  known,  since  the  two  series  are  not  in  contact.  It  is 
believed,  however,  that  the  sedimentary  series  is  much  younger  than  the  schist  series, 
because  of  the  lithological  analogies  existing  between  the  two  series  and  corresponding 
series  in  the  Marquette  district. 

Moreover,  within  the  Algonkian  series  there  is  an  unconformity  which  is 
revealed  by  the  presence  of  a  coarse  quartzite  containing  pebbles  of  jasper,  which 
must  have  been  furnished  by  beds  under  the  quartzite.  No  such  l)eds  in  this  strati- 
graphic  position  are  now  known  to  exist  in  the  district,  and  hence  it  is  assumed  that 
thej'  have  been  removed  by  erosion,  and  that  a  portion  of  their  debris  is  now  incor- 
porated in  the  quartzites.  This  unconformity  corresponds  with  that  Ijetween  the 
Upper  Marquette  and  the  Lower  Marquette  in  the  Marquette  district,  and  between 
the  Upper  and  Lower  Huronian  in  the  Crystal  Falls  area.  In  this  district  the  two 
series  are  called  the  Lower  Menominee  and  the  Upper  Menominee. 

Section  1.  The  Lower  Menominee  series  is  sul)divided  from  the  base  upward 
into  three  formations— the  Sturgeon  quartzite,  the  Randville  dolomite,  and  the 
Negaunee  formation  (iron  bearing). 

The  Sturgeon  quartzite  is  found  only  along  the  northern  side  of  the  Menominee 
trough,  where  it  forms  a  southward-dipping  monocline  bordering  the  south 
side  of  the  Archean  complex,  and  separated  from  it  by  an  unconformity.  Its 
topography  is  rugged.  At  its  base  the  formation  consists  of  conglomerates 
composed  largely  of  the  debris  of  granite  and  gneiss.  These  grade  upward  into 
quartzites  through  arkoses  and  graywackes.  The  conglomerates,  the  arkoses,  and 
the  graywackes  are  nearly  always  schistose,  but  the  quartzites  are  practically  alwaj^s 
massive.  This  difference  in  structure  is  explained  as  due  to  the  fact  that  the 
conglomerates,  arkoses,  and  graywackes  are  nearer  the  contact  plane  with  the 
underlying  Archean  than  the  quartzites,  and  hence  were  nearer  the  zone  of  accom- 
modation in  which  movement  occurred  during  the  folding  of  the  district. 

The  quartzites  are  principally  white  vitreous  or  saccharoidal  varieties,  composed 
of  plainly  fragmental  quartz  grains  that  often  are  enlarged  by  the  addition  of  quartz 
on  their  peripheries.  A  few  schistose  quartzites  differ  from  the  predominant  massive 
varieties  in  containing  much  sericite.  At  the  top  of  the  formation  the  quartzites 
pass  into  dolomitic  quartzites,  and  these  in  turn  grade  into  quartzose  dolomites  at 
the  base  of  the  Randville  dolomite. 

The  major  folding  of  the  quartzite  is  simple.  Within  the  formation  a  few 
divergencies  of  sti'ike  and  dip  are  noted,  l)ut  in  the  main  tlie  beds  are  nearly  vertical. 
They  constitute  one  limb  of  a  synclinorium,  the  other  limb  of  which  should  appear 
adjacent  to  the  southern  area  of  Quinnesec  schists,  and  also  around  the  western  area. 
Its  absence  from  these  positions  is  supposed  to  be  the  result  of  the  erosion  which 
intervened  between  Lower  Menominee  and  Upper  Menominee  time.  At  the  western 
end  of  the  district  the  quartzite  belt  turns  northward  around  the  end  of  the  Archean 


22  OUTLINE  OF  MONOGRAPH. 

anticline,  separating  the  Menominee  from  the  Calumet  tongue.  At  this  turn  it  is 
folded  into  a  number  of  synclines  and  anticlines  pitching  west. 

The  thickness  of  the  formation  is  estimated  to  be  between  1,000  and  1,250  feet. 
The  most  interesting  occurrences  of  the  quartzite  are  to  be  found  at  the  rock  dam  on 
Pine  Creek  and  at  the  falls  of  Sturgeon  River. 

The  Randville  dolomite  is  identical  with  a  similar  dolomite  series  in  the  Felch 
Mountain  and  the  Crystal  Falls  districts.  It  occupies  three  belts,  called,  respec- 
tively, the  northern,  the  central,  and  the  southern.  The  northern  belt  lies  immedi- 
ately south  of  the  Sturgeon  quartzite,  in  the  valley  of  Pine  Creek.  Few  exposures 
have  been  seen,  as  the  area  underlain  by  the  belt  is  covered  with  the  sands  distributed 
by  the  stream.  The  central  belt  is  narrow,  it  occupies  the  axis  of  the  trough 
extending  from  a  point  north  of  Lake  Antoine  eastward  to  the  bluff  known  as  Iron 
Hill,  in  sec.  32,  T.  40  N.,  K.  29  W.  The  southern  and  most  important  belt  stretches 
from  a  point  near  the  Menominee  River,  west  of  Iron  jNIountain,  eastward  to  the  end 
of  the  district,  where  it  is  lost  under  a  covering  of  Paleozoic  sediments.  The  most 
important  mines  of  the  district  are  just  south  of  its  southern  border.  On  account  of 
its  resistant  nature  the  dolomite  in  the  southern  belt,  and,  to  a  less  extent,  that  in 
the  central  belt,  gave  rise  to  the  elevations  which  stretch  through  the  district  in  the 
form  of  the  two  ridges  already  mentioned,  and  which  are  explained  as  residuals  of  a 
plain  once  existing  over  the  entire  Menominee  area. 

The  dolomite  formation  comprises  an  interbedded  series  of  dolomites,  quartzose 
dolomites,  dolomitic  quartzites,  dolomitic  slates,  cherty  quartzites,  and  talcose  schists. 
The  dolomites  predominate.  At  the  base  of  the  series  they  are  more  or  less  richly 
quartzose.  The  cherty  quartzites  are  fine-grained  cherty  rocks  that  are  usually  brec- 
ciated.  In  color  thej'  varj'  somewhat,  but  white  and  red  shades  are  most  prevalent. 
These  rocks  occur  in  but  a  few  places,  but  always  above  the  dolomites.  Their 
absence  from  much  of  the  region  is  accounted  for  by  the  erosion  which  removed 
them  from  over  the  most  exposed  portions  of  the  surface  during  the  interval  between 
the  Upper  and  Lower  Menominee  epochs.  The  slates  are  light-colored  talcose  and 
sericitic  varieties.  They  are  not  very  prominent.  Occasionally  they  are  found  well 
down  in  the  series,  but  usually  they  are  limited  to  its  upper  portions,  where  they  are 
in  contact  with  closely  similar  slates  belonging  in  the  Upper  Menominee  series.  The 
talcose  schists  have  been  observed  only  at  the  upper  contacts  of  the  Randville  forma- 
tion, where  the  purer  dolomites  are  immediately  beneath  the  basal  layers  of  the 
Upper  Menominee  rocks,  and  more  laarticularly  in  places  where  severe  folding  has 
taken  place.  They  are  soft,  dark,  much-jointed  rocks,  composed  largely  of  serpen- 
tine and  talc.  They  were  formed,  in  all  probability,  in  consequence  of  the  fact  that 
the  dolomites  were  in  a  zone  of  movement  where  the  conditions  were  favorable  to 
active  chemical  processes.  In  many  places  the  dolomites  were  crushed  into  breccias, 
and  at  one  place.  Iron  Hill,  a  well-defined  dolomitic  conglomerate  occurs. 

The  cherts  of  the  Randville  dolomite  are  identical  in  character  with  those  in  the 
Gogebic  and  Mai-quette  districts  and  have  the  same  stratigraphic  position  as  these. 
In  all  three  districts  they  are  supposed  to  be  of  organic  origin. 


OUTLINE  OF  MONOGRAPH.  23 

The  folding  of  the  Randville  dolomite  "is  the  key  to  the  knowledge  of  the 
folding  of  the  entire  series  of  Algonkian  rocks  in  the  district."  The  formation 
occui's  as  a  monocline  in  the  northern  belt  and  as  anticlines  in  the  central  and 
southern  belts.  The  northern  belt  follows  closely  the  distribution  and  the  folding  of 
the  Sturgeon  quartzite.  The  central  belt  is  the  top  of  an  anticline  which  is 
connected  with  the  northern  and  the  southern  belts  by  synclines.  It  is  terminated  at 
both  ends  by  plunging  beneath  the  overlying  beds.  At  its  east  end  the  eastward 
plunging  anticline  is  plicated  into  several  minor  folds.  Thus  the  central  belt  is 
aflected  by  a  broad  anticline  with  a  north-south  axis,  as  well  as  by  a  narrow  one 
with  an  axis  trending  a  little  north  of  west.  The  west  end  of  the  southern  belt  must 
likewise  end  in  a  plunguig  anticline,  as  slates  of  the  Hanbury  formation  are  known 
to  occur  a  few  miles  west  of  the  Menominee  River  on  the  strike  of  its  trend.  Its 
east  end  disappears  under  Paleozoic  beds.  The  south  side  of  the  syncline,  which 
must  exist  to  the  south  of  this  belt  if  its  structure  is  anticlinal,  would  be  exjjected 
on  the  north  side  of  the  southern  Quinnesec  schists.  Its  absence  from  this  position 
and  from  the  border  of  the  western  area  is  explained  in  the  same  way  as  is  the 
absence  of  the  Sturgeon  quartzite  from  these  stretches  of  country. 

The  dolomite  in  all  three  belts  is  closely  plicated  by  folds  of  high  oi'ders.  Those 
of  the  second  order  are  important  from  an  economic  point  oj:  view,  because  they 
determined  the  positions  of  the  great  ore  deposits.  These  folds  express  themselves 
in  the  interiors  of  the  dolomite  areas  by  causing  variations  in  the  strikes  and  dips  of 
neighboring  beds.  On  the  margins  of  the  areas  they  are  exhibited  as  indentations  in 
the  boundaries  of  the  belts.  These  are  best  seen  along  the  borders  of  the  southern 
belt  and  more  particularly  on  its  southern  side.  Beginning  at  the  west,  the  most 
important  of  these  marginal  folds  have  been  called  the  Walpole,  the  Pewabic,  the 
Quinnesec,  the  Norway,  the  Aragon,  and  the  West  Vulcan  folds,  because  within 
them  are  situated  the  great  mines  of  the  same  names.  There  are  other  less  important 
folds  along  this  southern  border,  and  in  addition  there  are  known  to  be  several 
important  ones  on  its  northern  border.  Exposures  are  rare,  however,  on  the  north 
side  of  the  southern  belt,  and  there  is  therefore  much  difficulty  in  recognizing  the 
folding.  Each  of  the  folds  is  described  and  the  reasons  for  regarding  them  as  folds 
are  given  in  detail.  In  the  western  portion  of  the  area  all  the  marginal  folds  pitch 
west;  at  the  east  end  of  the  district  they  pitch  east,  thus  confirming  the  view  that 
the  district  as  a  whole  is  affected  by  a  broad  cross  anticline  as  well  as  by  a  more 
cotnpressed  longitudinal  syncline. 

The  thickness  of  the  formation  is  probably  somewhere  between  1,000  and 
1,500  feet. 

The  dolomite  series  is  nowhere  seen  in  actual  contact  with  the  underlying  Stur- 
geon quartzite,  but  the  gradation  observed  at  the  top  of  this  formation,  together  with 
the  gradation  of  the  purer  dolomites  into  quartzose  phases  at  the  base  of  the  dolomite 
formation,  indicates  that  the  two  pass  into  one  another  through  dolomitic  quartzites. 
Above,  the  dolomite  may  have  passed  into  the  Negaunee  formation  through  the 


24  OUTLINE  OF  MONOGRAPH. 

cherty  quartzites,  Init  since  no  i-ocks  belonging  to  the  Negaunee  formation  remain  in 
the  Menominee  district  the  exact  nature  of  the  transition  is  not  known.  In  most 
places  the  uj^per  contact  of  the  RandviUe  dolomite  is  with  the  members  of  the  Upper 
Menominee  series.  When  the  overlying  formation  is  the  basal  member  of  the  series — 
that  is,  when  the  contact  is  with  the  Vulcan  formation — the  transition  between  the 
two  is  sudden.  Thei'e  is  no  recognizable  structural  unconformit}'  between  them,  but 
at  the  base  of  the  upper  series  there  is  usuall}-  a  conglomerate  or  coarse  quartzite 
containing  pebbles  of  chert  and  jasper  that  must  have  been  derived  from  some 
formation  beneath.  Their  existence  is  regarded  as  proof  that  there  was  once  above 
the  dolomite  a  jaspilite  formation,  like  the  Negaunee  formation  in  the  Marquette 
district.  Thus,  it  is  believed,  there  was  an  erosion  interval  preceding  the  deposition 
of  the  Vulcan  i-ocks  and  at  some  time  during  the  period  when  erosive  agents  were  at 
work  the  RandviUe  dolomite  formed  a  land  surface. 

In  many  jjlaces  the  dolomite  is  in  contact  with  the  Hanbury  slate,  which  normallj' 
lies  above  the  Vulcan  beds.  This  is  the  case  at  one  place  on  the  southern  side  of  the 
southern  belt  and  very  generally  along  its  northern  side.  It  is  also  the  case  at  the 
east  end  of  the  central  belt,  and  possibly  along  its  northern  side.  The  absence  of  the 
Vulcan  beds  from  those  places  at  which  it  would  noruiallj'  be  expected  to  occur  is 
explained  as  the  result  of  overlap  along  a  sinking  shore. 

At  a  number  of  places  along  the  contact,  especially  where  the  contact  is  between 
the  dolomite  and  the  Vulcan  beds,  the  rocks  on  both  sides  of  the  contact  line  are 
severely  brecciated.  Both  the  underh'ing  and  the  overlying  beds  are  shattered  and 
the  line  between  them  is  often  completelj'  obliterated. 

The  Negaunee  formation  is  represented  in  the  district  only  by  the  pebbles  in  the 
quartzite  at  the  base  of  the  Upper  Menominee  series.  There  are  a  few  jaspilites  near 
the  Curry  mine,  however,  that  are  slightly  different  from  most  of  the  corresponding 
rocks  in  the  Vulcan  beds.  Since  their  jasper  layers  are  identical  in  character  with 
the  jasper  pebbles  in  the  quartzite,  these  jaspilites  are  described  as  affording  a  fair 
idea  of  the  nature  of  the  Negaunee  beds  that  formerly  must  have  existed  in  the 
district. 

Section  2.  The  Upper  Menominee  series  comprises  all  the  beds  between  the  top 
of  the  RandviUe  dolomite  and  the  bottom  of  the  Lake  Superior  sandstone.  It 
includes  two  formations — the  Vulcan  formation  (iron  bearing)  and  the  Hanbury  slate. 

The  reason  for  the  separation  of  this  series  from  the  Lower  Menominee  series  is 
the  presence  of  a  stratigraphical  lireak  between  the  RandviUe  dolomite  and  the  bottom 
of  the  Vulcan  formation. 

The  rQcks  of  the  Upper  series  occupy  the  synclinal  areas  between  the  anticlines 
of  dolomite  and  those  between  the  dolomite  and  the  two  areas  of  Quinnesec  schists. 
From  the  distribution  of  the  series  it  is  clear  that  it  must  occur  in  three  sj'nclines 
and  two  anticlines  with  east-west  axes  and  the  same  number  of  similar  folds  with 
north-south  axes. 

Since  the  Vulcan  formation  occurs  immediately  above  the  dolomite,  it  should 
surround  the  dolomite  areas  in  a  continuous  belt  under  normal  conditions.     At  many 


OUTLINE  OF  MONOGRAPH.  25 

places,  howevei',  the  rocks  of  the  Vulcan  formation  are  hacking-  in  this  situation,  and 
the  Hanbury  slate  occupies  the  position  thej'  would  naturall}-  be  expected  to  occupj'. 
Wherever  found,  liowever,  the  Vulcan  beds  always  lie  between  the  dolomite  and  the 
slate.  The  lack  of  continuitj'  of  the  Vulcan  belt  is  ascribed  to  overlap  of  the  Hanbury 
slate. 

Lithologically  the  Vulcan  formation  is  separable  into  three  members,  which  are, 
in  ascending  order,  the  ore-bearing  Traders  member,  the  Brier  slate,  and  the  ore- 
bearing  Curi'v  member.  The  first  comprises  slates,  conglomerates,  quartzites,  and 
jaspilites;  the  second  is  composed  exclusively  of  slate,  and  the  third  consists  of 
jaspilites  and  slates.     Ore  deposits  occur  in  both  the  Traders  and  the  Currj-  beds. 

The  Traders  member  is  not  as  widelv  distributed  as  the  other  two  members  of 
the  formation.  Where  one  member  is  absent,  it  is  the  Traders  member.  Although 
this  is  not  as  continuous  as  the  other  members,  nearly  all  the  large  mines  of  the 
district  obtain  their  ores  from  its  deposits. 

The  slates  of  the  Traders  member  are  always  found  in  its  liasal  portions,  where 
they  are  associated  with  quartzites  and  conglomerates.  These  are  usually  light- 
colored  phases  that  are  with  great  difficult}''  distinguishable  from  some  of  the  talcose 
slates  at  the  top  of  the  Randville  dolomite.  In  a  few  places  the  slates  are  black, 
heav}^  varieties  that  are  merely  verj'  quartzose  fragmental  ores.  The  light-colored 
slates  grade  into  the  quartzites  and  conglomerates.  The  latter  rocks  contain  abundant 
jasper  and  ore  pebbles.  Where  these  constitute  the  main  portion  of  the  deposits  the 
rocks  pass  into  jaspilites,  which  are  banded  rocks,  composed  of  alternating  lavers 
of  I'ed  jasper  and  black  ore.  When  the  structure  of  the  jaspilites  is  fairly  coarse, 
the  small  grains  of  jasper  and  ore  composing  them  can  be  distinguished  on  their 
bedding  surface  as  small  oval  areas,  producing  a  distinct  mottling.  Where  shearing 
has  taken  place  the  ore  bands  have  been  rendered  schistose,  or  micaceous,  producing 
specular  ores,  and  the  jasper  bands  have  been  mashed  so  that  the  tinj'  grains  of 
jasper  have  assumed  lenticular  shapes.  In  some  places  brecciation  has  occurred, 
and  the  rock  is  now  a  mass  of  jasper  fragments  in  an  ore  matrix.  Much  of  the 
material  in  the  Traders  jaspilites  is  thus  of  fragmental  origin.  In  addition  to  the 
fragmental  material  in  them,  however,  there  is  also  much  crystallized  quartz  and  a 
good  deal  of  newly  deposited  hematite.  As  the  grain  becomes  finer  the  fragmental 
structure  of  both  jasper  and  ore  disappears,  the  quantity  of  secondarily  deposited 
quartz  and  hematite  increases,  and  the  jaspilites  become  more  like  the  typical  jaspi- 
lites of  the  Marquette  area,  which  were  formed  mainly  by  the  decomposition  of  a 
cherty,  ferruginous  carbonate. 

Under  the  microscope  a  few  nodular  masses  of  jasper  and  ore  are  observed  in 
thin  sections  of  the  Traders  rocks,  and  these  are  thought  to  lie  pseudomorphs  of 
siderite  or  greenalite  concretions.  Their  presence  is  evidence  that  some  of  the  silica 
and  hematite  in  the  Menominee  jaspilites  was  derived  from  an  iron  carbonate  by 
metasomatic  replacements.  In  all  cases  the  ore  bands  differ  from  the  jasper  bands 
mainly  in  the  greater  abundance  of  their  ferruginous  component. 


26  OUTLINE  OF  MONOGRAPH. 

The  Brier  slate  is  an  even-banded,  heavy,  blacJs  slate,  occupying  a  belt  of 
country  adjacent  to  the  Traders  jaspilites.  The  rock  consists  of  quartz  grains  and 
hematite  crystals,  embedded  in  a  matrix  composed  of  quartz,  decomposed  feldspar, 
kaolin,  and  a  little  chlorite.  Here  and  there  are  a  few  large  plates  of  brown  biotite 
and  white  muscovite.  Some  specimens  contain  a  great  deal  of  dolomite.  The  Brier 
slate  grades  into  the  jaspilites  of  the  Curry  member  through  increase  in  the  quantity 
of  crystallized  silica  in  the  matrix  and  decrease  in  the  amount  of  fragmental  quartz 
present. 

The  Curry  member  is  probably  more  widely  distributed  than  either  the  Traders  or 
the  Brier  member.  It  is  found  in  all  places  where  any  portion  of  the  Vulcan  beds  have 
been  discovered.  Lithologically  the  member  is  an  even-bedded  series  of  jaspilites  and 
quartzose  slates,  besides  ore  deposits.  Of  the  jaspilites  two  varieties  are  recognized. 
In  one  the  jasper  is  dark  red  or  purple  and  very  fine  textured  and'the  ore  a  dense  black 
hematite.  These  are  very  like  the  Traders  jaspilites.  In  the  other  variety  the  jasper 
may  be  dark  red,  pinkish,  or  white.  Both  the  jasper  and  the  ore  are  sandy  textured 
and  look  as  though  made  up  largely'  of  loosely  cohering  grains.  When  examined 
microscopicall}'  the  sandj'  jaspers  are  found  to  contain  manj'  oval  and  round  masses 
of  cherty  quartz,  surrounded  by  narrow  zones  of  hematite  and  embedded  in  a  finely 
crystalline  aggregate  of  quartz.  In  the  ore  layers  the  zones  of  hematite  around  the 
chert  nuclei  are  very  broad,  and  the  interstitial  quartz  is  small  in  quantity.  The 
quartzose  slates  differ  from  the  jaspilites  in  being  more  homogeneous.  The}*  con- 
sist of  a  series  of  very  thin  alternating  siliceous  and  ore  layers,  so  that  there  is  little 
or  no  distinction  between  ore  and  jasper  bands.  These  rocks  are  found  at  the  base 
of  the  Currj'  member,  and  are  in  a  way  gradation  phases  between  the  Curry  jaspi- 
lites and  the  Brier  slates. 

The  oval  masses  in  the  sandy  phases  of  the  Curr}^  jaspilites  are  much  more 
numerous  than  thej"  are  in  the  Traders  jaspilites.  As  in  the  case  of  the  Traders 
rocks,  they  are  believed  to  be  pseudomorphs  of  siderite  or  greenalite  concretions. 
They  are  similar  in  all  respects  to  the  concretions  that  have  been  described  in  the 
Gogebic  and  Marquette  jaspers  and  in  the  Mesabi  and  Gunflint  Lake  cherts.  In  the 
vicinitj'  of  the  Curry  mine  all  the  rocks  of  the  Curry  member  are  cut  by  veins  of  red 
crystalline  dolomite,  and  the  ores  are  saturated  with  the  same  material  to  such  an 
extent  that  their  siliceous  component  has  entirelj-  disappeared,  and  in  its  place  is  a 
matrix  of  dolomite. 

Where  no  marked  disturbances  in  their  relations  exist  the  members  of  the 
Vulcan  formation  grade  into  each  other  by  transition  forms.  Where,  on  the 
contrary',  the  members  are  closely  folded  the  contact  between  the  Traders  and 
the  Brier  members  is  often  sharp,  and  the  rocks  on  both  sides  of  the  contact 
line  are  severely  brecciated.  This  is  true  at  the  Norway  mine  and  in  the  Curry 
location.  Subsequently  hematite  was  deposited  in  this  crushed  zone,  producing 
marketable  ores. 

The  Vulcan  formation  is  a  succession  of  beds  laid  down  in  water.  The  lower 
beds  are  largely  fragmental,  although  intermingled  with  the  fragmental  material 


OUTLINE  OF  MONOGRAPH.  27 

there  must  have  been  some  cherty,  ferruginous  material  that  had  been  precipitated 
chemically.  In  some  places  the  mechanical  sediments  were  in  great  excess.  In 
other  places  the  chemical  sediments  appear  to  have  predominated.  In  the  course  of 
time  the  latter  were  changed  to  crystalline  quartz  and  hematite  through  the  agency 
of  descending  meteoric  waters,  and  the  mass  was  enriched  by  deposits  of  hematite 
between  the  original  grains. 

After  the  Traders  beds  had  been  laid  down  to  a  thickness  of  several  hundred 
feet  in  some  places  the  conditions  of  deposition  changed.  The  cherty  material 
ceased  to  be  precipitated,  and  the  Brier  slates  were  laid  down.  At  the  end  of  Brier 
time  the  conditions  that  prevailed  at  the  end  of  Traders  time  recurred,  and  chemical 
sediments  were  again  precipitated.  In  this  period  they  were  less  contaminated  with 
fragmental  material.  The  abundance  of  concretionary  ore  in  the  Curry  beds  shows 
that  some  of  these  must  have  consisted  almost  exclusively  of  the  chemical  precipitate. 
Jaspilites  were  produced  from  the  carbonate  and  the  greenalite  in  the  same  manner 
as  in  the  Traders  beds,  and  some  of  these,  after  enrichment,  became  ore  Ijodies. 

The  major  folding  of  the  Vulcan  beds  follows  closely  the  folding  of  the 
subjacent  dolomite.  Within  the  formation,  however,  the  beds  are  crumpled  and 
crinkled  into  small  folds,  and  upon  these  are  superposed  still  smaller  flutings. 

Wherever  folding  is  observed  it  is  best  preserved  in  the  jasper  bands.  The  ore 
layers  between  these  were  sheared  and  made  schistose.  Where  the  folding  was  very 
severe  both  ore  and  siliceous  layers  developed  a  slaty  cleavage.  In  some  places  the 
jasper  was  fractured  and  a  breccia  of  jasper  fragments  in  a  micaceous  ore  matrix 
resulted. 

The  total  thickness  of  the  Vulcan  formation  averages  about  650  feet,  divided  as 
follows:  Traders  member,  150  feet;  Brier  slate,  330  feet;  Curry  member,  170  feet. 
The  Brier  and  Curry  members  maintain  an  almost  uniform  thickness  in  all  portions 
of  the  district  where  they  have  been  encountered.  The  Traders  member,  however, 
varies  widely  in  thickness,  as  would  be  expected  of  a  series  of  beds  deposited  against 
a  shore. 

The  relations  of  the  Vulcan  beds  to  the  underlying  Randville  dolomite  are  those 
of  a  younger  series  to  an  older  series,  where  the  two  are  not  separated  by  a  structural 
unconformity.  That  the  Vulcan  beds  were  laid  down  on  a  shore  composed  partly  of 
the  dolomite  is  shown  by  the  presence  of  dolomite  bowlders  within  the  iron  formation 
on  the  seventh  and  eighth  levels  of  the  Chapin  mine.  Their  relations  with  the  over- 
lying Hanbury  slates  are  those  of  complete  conformity. 

In  a  few  places  the  Hanbury  slate  is  against  the  dolomite,  the  Vulcan  beds  being 
nowhere  present  in  the  vicinity.  This  is  true  east  of  Quinnesec  and  at  the  east  end 
of  the  central  dolomite  belt.  It  is  also  believed  to  be  true  at  a  number  of  other 
places  where  the  slate  and  the  dolomite  series  have  not  been  seen  in  actual  contact 
or  in  exposures  very  close  to  one  another.  Faulting  of  the  slate  beds  over  the 
iron-bearing  beds  will  not  explain  the  phenomenon,  because  faulting  is  of  minor 
importance  in  the  district.     The  only  explanation  that  suggests  itself  to  account  for 


28  OUTLINE  OF  MONOGRAPH. 

all  the  facts  of  distribution  of  the  Vulcan  and  the  Hanbury  formations  is  that  of 
unconformity  between  the  Lower  Menominee  and  the  Upper  Menominee  sei'ies, 
with  a  gradual  advance  of  the  Upper  Menominee  sea,  the  deposits  of  which  slowlj' 
overlapped  the  earlier  deposits  and  gradualh"  buried  the  higher  lands  composed  of 
the  Lower  Menominee  rocks. 

The  Traders  and  the  Curry  ores  are  not  very  different.  Practically  all  are 
of  Bessemer  grade,  though  some  are  highly  siliceous  and  others  contain  but  little 
silica.  The  former  are  especialh'  rich  portions  of  the  jaspilites  that  have  had  their 
ferruginous  component  increased  by  processes  of  enrichment.  These  lean  ores 
differ  very  little  in  appearance  from  the  jaspilites,  of  which  they  are  essentiallj^  a 
pail.  They  are  banded,  brecciated,  and  often  specular.  The  brecciated  ores  may 
consist  of  jasper  fragments  in  a  mass  of  hematite,  or  of  hematite  fragments  in  a 
mass  of  dolomite,  or  they  may  be  composed  of  fragments  of  ore.  jasper,  and  slate  in 
a  mass  consisting  largely  of  slate  debris  that  has  been  strongly  ferruginized. 

The  rich  ores  are  usually  liluish-black,  porous,  rine-grained  aggregates  of  crys- 
tallized hematite,  occurring  in  the  troughs  of  pitching  folds  or  in  other  situations 
toward  which  descending  water  is  likely  to  be  directed.  Comparisons  of  analyses  of 
all  the  ores  of  the  district  show  them  to  consist  principally  of  hematite,  with  addi- 
tional varying  amounts  of  magnetite,  silica,  alumina,  lime,  magnesia,  carbon  dioxide, 
phosphorus  pentoxide,  and  water.  Most  of  the  ores  contain  also  manganese,  potash, 
and  soda,  and  a  few  of  them  titanium  and  carbon.  The  mininumi  silica  reported  in 
the  ores  of  1900  is  2.75  per  cent  and  the  maximum  38.65  per  cent.  Twelve  analyses 
of  cargoes  of  typical  ores  are  given  and  four  complete  anah'ses.  The  latter  indicate 
that  tlie  richer  ores  are  mixtures  of  hematite,  magnetite,  muscovite,  serpentine, 
dolomite,  apatite,  pj'rite,  quartz,  and  some  manganese  oxide. 

All  the  minerals  occurring  as  constituents  of  the  ores  are  found  also  as  visible 
masses  either  in  veins  cutting  the  ore  bodies  or  in  vugs  or  pores  within  them. 
Dolomite,  calcite,  and  pyrite  sometimes  exist  in  excellent  crystals,  and  serpentine  as 
large,  white,  almost  pure  masses.  Talc  also  occurs  in  thick  seams  of  almost  ideal 
purity,  and  chalcop3'rite  in  small  crystals  associated  with  pyrite.  The  carbonates 
and  sulphides  are  found  near  water  coui'ses  and  the  silicates  mainly  in  the  lower 
portions  of  the  ore  bodies. 

The  ores  when  exposed  to  the  action  of  the  atmosphere  become  coated  with  a 
white  elflorescence,  consisting  of  a  mixture  of  the  sulphates  of  sodium,  magnesium, 
and  calcium,  in  which  the  ffrst  named  is  gi'eatly  in  exces.s. 

The  larger  ore  deposits  all  rest  upon  relatively  impervious  foundations,  which 
are  in  such  positions  as  to  constitute  jjitching  troughs.  Within  this  district  such 
pitching  troughs  may  be  made  by  (1)  the  marginal  folds  in  the  Randville  dolomite; 
{■2)  the  slate  forming  the  bottom  part  of  the  Traders  memlier;  and  (3)  the  Brier  slate 
beneath  the  Curry  l)eds.  The  dolomite  is  especially  likely  to  furnish  a  suitable  basin 
for  the  accumulation  of  ore  bodies,  where  its  upper  member  has  been  transformed 
into  a  talcose  schist. 


OUTLINE  OF  MONOGRAPH.  29 

Smaller  ore  bodies  may  occur  at  contacts  between  the  different  members  of  the 
Vulcan  formation  and  at  places  within  the  iron-bearing-  member  where  severe 
brecciation  has  occurred. 

The  forms  of  the  ore  bodies  var}'  with  their  positions.  While  verj^  irregular  in 
shape  they  nevertheless  conform  in  a  general  way  to  the  shape  of  the  foundation  on 
which  they  rest.  The  deposits  in  troughs  have  in  general  a  U-shajied  cross  section, 
very  thick  at  the  bottom.  Where  much  compressed,  the  arms  of  the  U  may  unite  at 
the  center  and  produce  a  lens-shaped  deposit.  Contact  deposits  are  usually  broad 
and  sheet  like,  with  irregular  pi-ojections  extending  from  their  upper  surfaces. 

From  the  distribution,  associations,  and  composition  of  the  ores  and  the  shapes 
of  the  ore  deposits  it  is  evident  that  the  ores  of  the  Menominee  district,  like  those  in 
the  Gogebic  and  Marquette  districts,  were  concentrated  by  descending  waters  flowing 
in  definite  channels.  A  portion  of  the  iron  oxide  in  the  Traders  member  is  of  frag- 
mental  origin,  b^ing'the  debris  of  an  older  jaspilite  formation,  and  perhaps  a  portion 
of  that  in  the  Curry  member  had  a  similar  origin.  These  ferruginous  bodies,  how- 
ever, were  enriched  by  the  addition  of  hematitic  material  from  some  overlying 
stx-atum,  from  which  it  was  dissolved  by  meteoric  waters  and  transported  downward, 
finally  being  precipitated  between  the  fragmental  grains  of  the  original  sediments. 

The  processes  of  concentration  were  the  same  as  those  worked  out  b\'  Van  Hise 
for  the  Gogebic  and  the  Marquette  districts.  Oxj^genated  meteoric  waters  descending 
through  the  rocks  of  the  Hanbury  and  Vulcan  formations  dissolved  iron  carbonates 
and  silicates  and  precipitated  the  metal  as  oxide  in  or  near  the  position  of  the  original 
compounds.  Carbon  dioxide  was  thus  liberated  and  dissolved  in  the  descending 
waters.  These  took  up  more  iron  salts.  In  their  downward  passage  they  were 
converged  into  trunk  channels  by  plunging  synclines,  or  were  directed  into  definite 
courses  by  the  contact  planes  between  adjacent  beds  or  by  zones  of  brecciation.  At 
these  places  the  iron-bearing  waters,  which  necessarilj'  must  have  taken  cii'cuitous 
routes,  were  intermingled  with  water  which  had  descended  more  direct!}'  from  the 
surface,  and  which,  therefore,  had  retained  its  oxygen,  or  most  of  it.  Here  the 
dissolved  iron  carbonate  was  decomposed  and  iron  oxide  precipitated.  Thus  are 
found  pseudomoi'phs  of  hematite  in  place  of  original  ferruginous  concretions,  and 
great  deposits  of  ore  in  the  troughs  of  sjmclines  within  the  iron-bearing  formation. 
Continued  passage  of  water  along  the  same  channels  purified  the  deposits  by  removing 
from  them  deleterious  substances. 

Topographically  the  ores  are  usually  found  below  the  crests  of  hills,  on  their 
slopes  or  in  valleys  which  once  had  below  them  lower  valleys  in  which  the  descending- 
waters  may  have  found  an  outlet.  In  the  Menominee  district,  however,  this  relation 
between  the  position  of  ore  bodies  and  the  topography  is  not  as  clear  as  it  is  in  the 
other  Lake  Superior  iron  districts. 

The  beginning  of  the  concentration  of  the  ores  must  have  been  at  the  close 
of  Upper  Hui-onian  time,  that  is,  after  the  folding  of  the  Huronian  rocks.  It  was 
practically  completed  before  the  beginning  of  the  Upper  Cambrian. 


30  OUTLINE  OF  MONOGRAPH. 

A  critical  study  of  the  geological  relations  of  the  ore  deposits  of  each  of  the 
mines  in  the  district  indicates  that  all  deposits  of  any  magnitude  are  situated  in  just 
such  positions  with  respect  to  the  surrounding  rocks,  as  might  have  been  prophesied, 
on  the  assumption  that  they  were  accumulated  by  the  action  of  descending  ground 
water. 

The  Hanbury  slate  occupies  nearlj-  all  the  low  ground  within  the  Menominee 
trough.  It  occurs  in  three  synclinal  belts  lying  between  the  anticlines  of  dolomite 
and  between  the  southern  dolomite  belt  and  the  south  area  of  Quinnesec  schists. 
The  slate  belts  widen  toward  the  west  because  of  the  westward  plunging  of  the  entire 
synclinorium. 

The  formation  comprises  clay  slates,  calcareous  and  graphitic  slates,  graywackes, 
thin  beds  of  ferruginous  dolomite,  and  small  bodies  of  chert  and  hematite.  The 
formation  is  cut  by  a  few  greenstones  that  are  now  great!}'  decomposed. 

The  clay  slates  are  normal  rocks.  AVhen  sheared  and  much  weathered  they 
become  light-colored  sericite-schists.  Many  specimens  are  stained  red  in  irregular 
patches,  producing  a  red  and  white  mottled  rock  known  locally  as  calico  slate. 
The  calcareous  and  graphitic  slates  appear  to  be  limited  to  the  lower  horizons  of 
the  formation,  the  former  being  nearly  always  associated  with  ore  bodies.  The 
quartzites  are  very  siliceous  dolomites.  The  cherts  and  hematite  are  usually  closely 
associated.  The  former  are  gray  or  white.  The  latter  is  a  dense-black  or  dark-brown 
variety.  Where  the  slates  are  cut  bj^  greenstone  they  have  suffered  some  contact 
metamorphism,  with  the  production  of  a  little  biotite  and  actinolite. 

The  folding  of  the  formation  is  very  complicated.  Folds  of  high  orders  are 
common — practically  universal.  In  the  eastern  portion  of  the  area  the  pitch  of  these 
small  folds  is  to  the  east  and  in  its  western  portion  to  the  west.  The  distribution 
of  the  folds  and  their  varying  pitches  corresponds  closely  to  the  major  folding  of  the 
district.  No  approximately  correct  estimate  of  the  thickness  of  the  slate  formation 
is  attempted,  because  of  the  difficultv  of  eliminating  the  effects  of  the  close  folding. 
It  is  safe  to  say,  however,  that  the  Hanburj'  formation  is  the  thickest  of  all  the 
formations  in  the  district. 

Like  the  other  members  of  the  Menominee  series,  the  slates  are  unconformably 
beneath  the  Lake  Superior  sandstone. 

No  workable  ore  deposits  have  thus  far  been  discovered  within  the  slate  area, 
but  there  are  seven  or  eight  places  at  which  lean  ores  have  been  obtained.  These 
are  widely  distributed.  Because  of  the  interest  naturally  attached  to  the  discovery 
of  ores  of  any  kind  in  the  gi'eat  slate  areas,  each  of  these  localities  is  briefly  described. 

It  is  possible  that  ore  deposits  of  workable  size  occur  in  the  slates  in  very 
favorable  situations,  though  no  indication  of  their  presence  has  j^et  been  observed 
in  this  district.  From  the  fact,  however,  that  large  deposits  are  known  to  exist  in 
the  Hanbury  slates  of  the  Florence,  Crystal  Falls,  and  Iron  River  districts,  it  is 
possible  that  similar  deposits  ma}'  occur  in  the  Menominee  district. 


OUTLINE  OF  MONOGRAPH.  31 

In  exploring  within  the  Hanbuiy  area  only  the  most  favorable  localities  need  be 
tested.  These  are  the  places  where  ferruginous  dolomites  occur,  where  the  rocks 
are  folded  or  brecciated,  and  where  the  folds  involve  au  impervious  stratum. 

Chapter  VI.  Above  the  folded  Algonkian  rocks  lie  the  horizontal  beds  of 
the  Paleozoic  sediments,  with  a  profound  unconformity  between  the  two  series.  The 
Paleozoic  series  comprises  the  Lake  Superior  sandstone  below  and  the  Hermans- 
ville  limestone  above.  These  once  extended  over  the  entire  district.  East  of 
Waucedah  they  still  cover  all  the  older  rocks,  but  west  of  this  place  they  are  now 
found  capping  only  the  higher  hills. 

The  Lake  Superior  sandstone  is  mainly  a  red  sandstone.  Its  thickness  is  esti- 
mated to  be  300  feet.  In  its  lower  portions  are  conglomerates,  which,  where  thej' 
lie  on  the  Vulcan  beds,  contain  ore  bowlders  in  such  quantitj^  that  they  may 
occasionally  become  sources  of  ore. 

Fossils  are  extremely  rare.  A  few  fragments  of  trilobites  and  a  few  shells  of 
brachiopods  have  been  found  in  a  few  places.  The  former  have  been  identified  as 
Dicellocephalus  misa  and  the  latter  as  Lingulepis  2}innifarmis.  They  indicate  the 
St.  Croix  horizon  of  the  Upper  Mississippian  series. 

The  Hermansville  limestone  is  a  sandstone  with  calcareous  cement,  interbedded 
with  pure  dolomite.  Its  maximum  thickness  is  about  100  feet.  The  series  is  of 
little  importance  within  the  limits  of  the  Menominee  district,  but  is  widely  spread 
farther  east.  Rominger  identified  it  as  corresponding  to  the  Chazy  and  Calciferous 
formations  of  the  Eastern  States. 

Chapter  VII.  This  chapter  contains  an  outline  of  the  geological  history  of  the 
district.  Comparison  of  the  succession  of  formations  in  the  Menominee  district  with 
the  succession  in  the  Marquette  and  the  Grogebic  districts  shows  that  the  geological 
history  of  the  three  districts,  while  alike  in  its  major  features,  was  very  different  in 
minor  features.  The  attempt  to  correlate  the  events  that  transpired  in  the  various 
iron-bearing  districts  of  the  Lake  Superior  region  is  left  for  a  succeeding  publication. 


U,  S.  GEOLOGICAL   SURVEY 


MONOGRAPH  XLVI       PL. I 


ULIUS  BIENiCO  LITH   r 


Iron,  ore  -bea/uu/  districts  for  whiiJt  dataU  rruifis 
hoh-e  d«gn  published  are  cnclosfd.  by  r«tt  lines 

1  MenomUiee 

2  Oyxtal  FriUx 

3  Mewiftiette 

4  Gogebic 

5  MesabL 

6  VwnUion 


ARCHEAN 


algo:nkian- 


HURONIAN 

nvtn 


KEWEKI'iA.WAN 

I     Ak 


.  POST-ALGOXKrAN 


Including  considerable       Imiuding  considerable 
areas  of  Algonkian  granite      areasofArchean 

(the  iron-bearing  series) 

GEOLOGIC  AL\P  OF  PART  OF  THE  LAKE  SUPERIOR  REGION 

SHOWING    RELATIVE    POSITION  OF  THE    MENOMINEE  AREA 

WITH  RESPECT  TO  OTHER  HURONIAN  AREAS 

Compiled  from  Official  maps  of  United  States,  Staie,and  Canadian  Surveys 

Sc  ale 


HrHONIAN 


Original  Huronum. 
Uartfliette  iron.-beartnff  serias 
Ct-vs(iil  FdlL^  iran-b«arUu/  svfes 
Afaioniineir  i/-an- bearing  series 
Wl'iconstn  Valt&'i'  series 
PmokM-GoqrAlr  ironb^orina  series 
BlaiitRt.'i'er  iron  beai-inif  scfitifs 
QiippeH'a.  VtUie^'  qaarrxtzts 
St  Lotus  series 
ifesabL  irort-betiruif/sertes 
Vermilion  tixm- bearing  series 
AiiunUcte  irorrbearuig  series 
Folded  sc/tiste  of  Canada. 


THE  MENOMINEE  IRON-BEARING  DISTRICT  OF 

MICHIGAN. 


By  William  Shirley  Bayley. 


CHAPTER  I. 

INTRODUCTION. 

Scope  and  date  of  ivorh  done. — The  present  report  is  an  account  of  the 
geology  of  that  portion  of  the  Menominee  district  bordering  the  Menominee 
River  on  the  Michigan  side.  The  district  lies  entirely  within  the  State  of 
Michigan,  its  western  extension  into  Wisconsin  not  being  discussed.  A 
preliminary  report  of  the  district,  accompanied  by  a  geological  map,  was 
published  in  the  year  1900  as  a  folio  of  the  Geologic  Atlas  of  the  United 
States." 

The  field  work  upon  which  the  report  is  mainly  based  occupied 
the  summer  of  1896.  In  this  I  was  assisted  in  the  geological  work  by 
J.  Morgan  Clements  and  Samuel  Weidman.  Since  this  I  have  twice 
visited  the  district  for  supplemental  work,  first  in  1899  and  again  in  1900. 

Acknoioledfpnents. — To  the  superintendents  and  engineers  of  the  mines 
in  the  district  the  Survey  is  under  many  obligations  for  the  numberless 
courtesies  afforded  the  field  parties  and  for  the  generous  manner  in  which 
they  have  allowed  the  use  of  mine  plats.  Some  of  these  have  been 
reproduced  as  illustrations  in  the  body  of  this  report.  All  have  been  of 
value  in  working  out  the  intricate  structure  of  the  district. 

«VanHise,C.  R.,  and  Bayley,  W.  S.,  Description  of  the  Menominee  district:  Geologic  Atlas  U.  S., 
folio  62;  U.  S.  Geol.  Survey,  1900. 

MON   XLVI— O-t 3  33 


34  ^  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

To  Messrs.  F.  A.  Janson,  of  the  Penu  Iron  Company;  G.  Helberg, 
of  the  Aragon  mme;  V.  S.  Hillyer,  of  the  Minnesota  Iron  Company;  and 
L.  M.  Hardenbiirgh,  formerly  of  the  Pewabic  mine,  special  thanks  are  due 
for  copies  of  maps  and  plats  which  were  prepared  especially  for  this  work 
and  furnished  to  the  author  gratuitously. 

Limits  of  the  Menominee  area. — The  Menominee  district  proper  is 
bounded  on  the  west  by  the  Menominee  River;  on  the  south  by  the  same 
river  and  the  south  line  of  the  northern  tier  of  sections  in  T.  38  N.,  Michi- 
gan; on  the  east  by  the  east  line  of  sees.  2,  11, 14,  23,  26,  and  35,  T.  39  N., 
R.  28  W.,  and  their  continuation  north  and  south,  and  on  the  north  by  the 
north  line  of  T.  40  N.,  Michigan.  On  the  general  map  (PI.  II)  the  area 
represented  includes  a  region  extending  8  miles  farther  north,  to  the  north 
side  of  the  second  tier  of  sections  north  of  the  south  line  of  T.  42  N.,  and 
as  far  west  as  the  west  line  of  Ts.  41  and  42  N.,  R.  30  W.  The  geological 
map  (PL  IX)  includes  only  the  area  of  the  Menominee  district  proper. 

Relations  to  other  iron-hearing  areas. — The  area  designated  above  as  the 
Menominee  district  proper  constitutes  a  tongue  of  sedimentary  deposits 
lying  between  a  granite  area  to  the  north  and  a  green  schist  area  to  the 
south.  This  tongue  is  the  southernmost  of  five  distinct  tongues  (see  map, 
PI.  II)  which  extend  eastward  from  the  great  central  area  of  Huronian 
deposits  in  Wisconsin  and  Michigan,  described  in  part  in  the  Crystal  Falls 
monograph."  The  five  tongues,  beginning  with  the  northernmost,  are  the 
Marquette  tongue,  discussed  in  the  Marquette  monograph;  the  Sagola  and 
the  Felch  Mountain  tongues,  treated  in  the  Crystal  Falls  monograph;  the 
Calumet  tongue;  and  the  Menominee  tongue.  Each  is  structurally  a  trough 
of  Huronian  sediments  lying  between  rims  of  Archean  granites,  gneisses, 
and  schists.  To  the  west  they  all  widen  out  into  the  bi'oad  expanse  of 
Huronian  sediments  referred  to  above.  To  the  east  all  except  the  Mar- 
quette tongue  plinige  beneath  Paleozoic  deposits.  The  Calumet  tongue 
runs  a  little  north  of  east  and  then  east  through  the  center  of  T.  41  N., 
R.  29  W.,  Michigan,  as  a  narrow  belt  a  mile  or  a  mile  and  a  half  in  width. 
At  the  east  side  of  the  township  it  widens  rapidly,  becoming  broader  and 
broader  until,  in  T.  41  N.,  R.  27  W.,  where  it  disappears  under  Paleozoic 
deposits,  its  width  measures  7  J  miles. 

a  Clements,  J.  M.,  and  Smyth,  H.  L.,  The  Crystal  Falls  iron-bearing  district  of  Michigan,  with  a 
chapter  on  the  Sturgeon  River  tongue  by  AV.  S.  Bay  ley,  and  an  introduction  by  C.  R.  Van  Hise:  Mon. 
'   U.  S.  Geol.  Survey,  vol.  36,  1899. 


U.  S.  GEOLOGICAL   SURVEY 


MONOGRAPH    XLV  I         PL. 


'in£se 

GENERAI.  OLTTLINE  MAP 

OK    THE 

RECilOX  liE'HVl'KN  TIIE  MFL\0\nNEE  RI\T':R 
AND  THE  NOUTH  SIDE  ()!•  FEl.CH  MOUNTAIN  DISTmCT.  MK'HIdAN  ^""^ 

SIIOWINO  I'dSITION  OK  THE  MENOMINEE  TROUGH  WIT 

KESPECT  TO  OTHER  HURONIAN  TROUGHS  TO  THE  NORTH 

Scale 


5  miles 


R.30W. 


INTRODUCTION.  35 

At  its  west  end  the  south  side  of  the  Calumet  tongue  merges  with  the 
north  side  of  the  Menominee  tongue.  Farther  east  the  two  tongues  are 
separated  by  an  elliptical  area  of  Arehean  rocks. 

Shape  and  sise  of  the  Menominee  tongue. — In  general  the  Menominee 
tongue  is  a  spindle-shaped  area  about  17  miles  long,  trending  about  N.  55  "^ 
W.  Its  narrowest  portion  is  in  the  middle,  in  the  vicinity  of  Vnlcan,  where 
it  measures  about  4  miles  in  width  from  its  contact  with  the  granite  on 
the  north  to  its  contact  with  the  green  schists  on  the  Menominee  River  on 
the  south.  To  the  east  it  widens  gradually  until,  in  the  eastern  2:)ortion  of 
R.  28  W.,  its  width  is  about  7  miles.  To  the  west  also  it  gradually  becomes 
wider  and  tinally  loses  its  identity  as  a  distinct  trough  at  about  the  center 
line  of  R.  30  W.,  where  it  merges  with  the  Calumet  trough,  and  extends 
into  the  wide  area  of  Huronian  sediments  to  the  west. 

At  its  eastern  end  the  characteristic  rocks  of  the  tongue  are  so  deeply 
buried  beneath  later  sediments  that  they  can  not  be  traced.  Lines  of  mag- 
netic attraction,  however,  have  been  obtained  east  of  the  eastern  limit  of 
the  district,  as  given  above,  and  these  are  taken  to  mean  that  the  Huronian 
sediments  continue  for  at  least  a  short  distance  beyond  the  places  where 
they  are  last  seen  on  the  surface. 

The  area  covered  by  the  tongue  measures  about  112  square  miles. 
The  whole  area  studied,  including  the  Calumet  tongue,  the  Archeau  area 
between  the  Calumet  and  Menominee  tongues,  and  the  narrow  strip  of 
green  schists  along  the  Menominee  River,  aggregates  about  261  square  miles. 
All  the  producing  mines,  however,  are  situated  within  the  Menominee 
tongue,  the  three  in  the  Calumet  tongue  having  been  idle  for  over  fifteen 
years.  The  geology  of  the  Calumet  area  will  be  discussed  in  another  jjubli- 
cation.     The  present  monograjih  deals  only  with  the  Menominee  tongue. 

Economic  importance  of  the  district. — In  1902  the  mines  of  the 
Menominee  trough  shipped  3,001,189  long  tons  of  ore,  and  since  the  first 
shipment  of  ore  from  the  Quiunesec  mine  in  1873  the  aggregate  shi23ments 
of  all  mines  to  the  close  of  1902  have  amounted  to  the  large  total  of  very 
nearly  29,000,000  long  tons.  Of  this  aggregate  by  far  the  larger  proportion 
of  ore  has  been  of  Bessemer  grade.  The  total  shijjments  from  the 
Marquette  district  to  the  end  of  1902  were  66,686,502  long  tons;  those 
from  the  Crystal  Falls,  Iron  River,  and  Felch  Mountain  districts  in 
Michigan,  and  the   Florence  district   in  Wisconsin,  taken  together,  have 


36  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

amounted  to  about  13,400,000  long  tons;  those  from  the  Gogebic  range  in 
Michigan  and  Wisconsin  to  37,818,274  long  tons;  those  from  the  Vermilion 
range  in  Minnesota  to  19,061,506  long  tons;  and  those  from  the  Mesabi 
range  in  the  same  State  to  53,747,807  long  tons.  It  will  thus  be  seen  that 
in  proportion  to  its  area  the  Menominee  trough  has  yielded  as  large  a 
product  as  any  other  of  the  Lake  Superior  districts,  with  the  exception  of 
the  Mesabi.  Since  the  discovery  and  development  of  the  Mesabi  district 
the  demand  for  low  phosphorus  and  high  silica  ores  to  serve  as  mixtures 
for  the  Mesabi  ores  has  so  largely  increased  that  many  lean,  low  phosphorus 
ore  deposits,  formerly  not  marketable,  now  find  a  ready  sale.  The 
Menominee  district  can  furnish  an  abundance  of  this  grade  of  ore,  so  that 
it  is  probable  that  the  importance  of  the  district  as  a  mining  center  will 
increase  rather  than  diminish  in  the  future. 

Previous  work  in  the  district. — The  only  detailed  geological  maps  of  the 
Menominee  trough  that  have  heretofore  been  published  are  those  of  Brooks" 
(PL  IV)  and  Wright,''  in  the  Geology  of  Wisconsin.  Irving"  published  a 
general  map  (PI.  V)  of  the  district  in  his  introduction  to  Dr.  Williams's 
bulletin  on  the  origin  of  the  Menominee  green  schists,  but  he  made  no 
claim  that  it  exhibits  more  than  the  generalized  structural  features  of 
the  district.  Wright's  map  shows  the  distribution  of  the  green  schists, 
some  of  the  iron-bearing  belts,  and  the  pre-Huronian  rocks  of  the  district, 
while  that  of  Brooks  exhibits,  in  addition,  the  location  of  all  the  ledges  of 
dolomite,  slate,  quartzite,  and  other  sedimentary  rocks  met  with  during  this 
author's  explorations.  Brooks  also  presents  a  structural  sheet  illustrating 
his  views  as  to  the  sequence  of  the  rock  series  and  the  character  of  the 
folding.  This  map  was  of  great  use  to  the  field  parties  of  the  United 
States  Geological  Survey,  since  it  enabled  them  to  make  systematic  plans 
for  the  survey  of  the  district  and  directed  their  attention  to  many  rock 
ledges  that  might  otherwise  have  been  overlooked. 

In  addition  to  the  works  and  reports  referred  to  above,  another  valua- 
ble report  on  the  district  is  that  of  Rominger."*     This  report,  like  that  of  the 

a  Geology  of  Wisconsin,  Survey  of  1873-1879,  vol.  3,  pt.  7,  by  T.  B.  Brooks,  and  pt.  8,  by  C.  E. 
Wright,  and  Atlas,  Pis.  XXVIII,  XXIX,  and  XXX. 

i  Ibid. 

c  Williams,  G.  H.,  The  greenstone-schist  areas  of  the  Menominee  and  Marquette  regions  of 
Michigan,  etc.,  with  an  introduction  by  R.  D.  Irving:  Bull.  U.  S.  Geol.  Survey  No.  62,  1890. 

''Rominger,  C,  Upper  Peninsula,  pt.  2,  Menominee  iron  region:  Geol.  Surv.  Mich.,  vol.  4,  1881, 
pp.  155-241. 


INTRODUCTION.  37 

same  author  on  the  geology  of  tlie  Marquette  district,  consists  mainly  of  a 
discussion  of  ledges  and  of  detached  statements  concerning  the  relations  to 
one  another  of  the  different  "rock  groups"  met  with.  It,  nevertheless,  was 
ot  great  value  in  the  prosecution  of  the  field  work  on  which  the  present 
volume  is  based,  since  it  called  attention  to  the  most  promising  exposures 
in  the  district  and  in  manj^  instances  afforded  clues  as  to  the  places  at  which 
relations  could  best  be  studied. 

The  reports  of  Brooks,  Wright,  Irving,  and  Rominger  are  referred  to 
more  at  length  in  the  following  chapter,  and  in  this  chapter  also  are  given 
abstracts  of  all  the  other  important  papers  in  which  the  geology  of  the 
district  has  been  discussed.  A  perusal  of  this  chapter  will  show  that  many 
facts  bearing  on  the  subject  have  gradually  been  accumulated;  but  that  in 
no  other  cases  tlian  those  mentioned  above  did  the  facts  known  concerning- 
the  distribution  of  the  different  formations  warrant  the  construction  of 
geological  maps  of  the  district. 

Method  of  work. — Most  of  the  field  work  on  which  this  monograph  is 
based  was  done  in  the  months  of  July,  August,  and  a  part  of  September, 
1896.  The  entire  area  whose  limits  have  been  outlined  above  was  cut  by 
north-south  traverses  at  intervals  of  one-tenth,  one-fourth,  one-half,  or 
three-fourths  of  a  mile,  or  1  mile,  according  to  the  intricacy  of  the  geology 
iu  different  parts  of  the  district  and  the  character  of  the  surface  exposed  to 
view.  In  those  portions  of  the  district  from  which  the  forest  and  undei'- 
growth  have  been  removed  the  traverses  were  at  greater  intervals  than  in 
those  portions  covered  by  dense  thickets  of  young  trees  and  brush.  In  the 
wide  expanses  of  slate  to  the  south  of  the  Chicago  and  Northwestern  Rail- 
road the  traverses  were  1  mile  apart.  In  those  portions  of  the  district  where 
the  different  rock  belts  are  closely  folded  traverses  were  made  every  quarter 
of  a  mile.  The  iron-bearing  belt  was  examined  thoroughly,  every  ledge, 
so  far  as  is  known,  and  every  mining  pit  having  been  studied  in  detail. 
The  same  careful  examination  was  made  of  the  contact  between  the  quartz- 
ite  at  the  base  of  the  sedimentary  series  and  the  crystalline  rocks  to  the 
north,  and  an  almost  equally  careful  search  was  made  for  a  contact  of  the 
slates  with  the  greenstones  to  the  south.  In  areas  where  exposures  are 
small  and  scattered,  north-south  magnetic  lines  were  run  every  half  mile. 

During  the  summers  of  1899  and  1900  two  other  visits  were  made  to 
the  district,  but  the  field  work  was  limited  to  the  study  of  relations,  to  the 


38  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

ruimiug  of  a  few  additional  magnetic  lines,  and  to  the  investigation  of  the 
structure  of  small  complicated  areas  and  the  study  of  the  mines.  The  work 
was  supplementaiy  to  that  of  1896,  and  was  intended  simply  to  fill  the  gaps 
left  by  the  earlier  survey. 

Though  the  topography  of  the  district  is  simple,  much  of  the  surface 
is  covered  with  a  thick  mantle  of  glacial  drift  through  which  ledges  of  the 
softer  rocks  rarely  penetrate.  Other  portions  are  covered  by  a  sheet  of 
sandstone  which  obscures  some  of  the  most  interesting  contacts.  Moreover, 
thick  growths  of  brush  hide  much  of  the  surface,  especially  in  the  northern 
and  eastern  portions  of  the  district.  The  detail  maps  show  the  character, 
the  position,  and  the  number  of  ledges  investigated,  and  it  is  from  the 
evidence  afforded  by  these  and  by  the  mine  plats  that  the  structure  of  the 
district  has  been  worked  out. 

Classification  of  formations. — The  rocks  of  the  Menominee  district  belong 
to  the  Archean,  Algonkian,  and  Paleozoic  systems.  The  oldest  series  of 
rocks  bordering  the  Menominee  tongue  comprises  various  schists,  gneisses, 
and  granites.  These  are  regarded  as  Archean.  Resting  unconformably 
upon  the  Archean  rocks  is  a  succession  of  Algonkian  sediments,  which  are 
divisible  into  a  Lower  Menominee  and  an  Upper  Menominee  series,  sepa- 
rated from  each  other  by  an  unconformity.  The  Paleozoic  rocks  comprise 
horizontal  Cambrian  sandstones  and  Ordovician  limestones.  These  occur 
in  patches  on  the  tops  of  the  hills,  capping  the  closely  folded  and  trun- 
cated Huronian  rocks.  Both  of  the  Menominee  series  are  divisible  into 
a  number  of  formations,  each  representing  a  time  during  which  the  condi- 
tions of  deposition  were  approximately  uniform.  Each  of  the  pre-Cambrian 
formations  has  been  named  and  is  represented  on  the  general  map  of  the 
district  (PI.  IX)  by  a  distinctive  color.  The  following  table  gives  a  list  of 
the  formations,  arranged  in  descending  order  according  to  age.  The  frac- 
tional formations,  or  members  of  the  Vulcan  formation,  are  represented  on 
the  detail  maps  and  are  separately  characterized  in  the  text,  but  they  are 
not  differentiated  on  the  general  map. 


INTRODUCTION. 


39 


Table  showing  the  mccession  of  formations  in  the  Menominee  district  and  their 
relations  to  gener'ol  geological  systems. 


Formation. 


Paleozoic . 


[Ordovician /„  .^^f'  JHermansville  limestone. 

[Cambrian Potadam Lake  Superior  sandstone. 


Algonliian . 


Unconformity. 
Upper  Menominee 


Hanbury  slate. 

Vulcan  formation,  subdivided  into  the  ore-bearing 

Curry   member,    Brier  slate,    and    ore-bearing 

Traders  member. 


Unconformity. 

{Negaunee  formation 
Randville  dolomite. 
Sturgeon  quartzite. 

Unconformity. 


Aichean. 


Ciranites  and  gneisses,  cut  by  granite  and  diabase 

dikes. 
Quinnesec  schists,  cut  by  acid  and  basic  dikes  and 

veins. 

Names  of  the  formations. — The  names  of  the  Upper  Menominee  forma- 
tions and  of  the  Archean  schists  are  taken  from  locaHties  in  the  district. 
The  names  of  the  Lower  Menominee  formations  are  those  of  formations  in 
adjacent  districts  ah-eady  reported  upon,  with  which  the  Menominee  forma- 
tions are  beheved  to  be  continuous.  Beginning-  at  the  bottom,  the  Quin- 
nesec schists  are  so  named  since  they  are  typically  developed  at  the  Big 
and  the  Little  Quinnesec  Falls  on  the  Menominee  River.  The  Sturgeon 
quartzite  is  so  called  because  this  formation  in  the  Menominee  district  has 
been  traced  almost  continuously  to  a  like  formation  in  the  Crystal  Falls 
district,  which  has  been  called  the  Sturgeon  quartzite."  The  Menominee 
dolomite  is  called  the  Randville  dolomite  because  it  has  been  practically 
connected  with  the  Randville  dolomite  of  the  Crystal  Falls  district.*  The 
assumed  iron-bearing  Lower  Menominee  formation  is  called  the  Negaunee 
formation  because  this  is  the  Lower  Huronian  iron-bearing  formation 
of  the  Marquette  district.  In  the  Menominee  district,  as  will  be  seen,  this 
formation  has  not  yet  been  identified,  although  its  presence  is  indicated 
by  the  character  of  the  basal  member  of  the  Upper  Menominee  series. 

In  the  Upper  Menominee  the  Vulcan  foi'mation  is  so  named  since  the 
iron  formation  occurs  in  typical  development,  with  full  succession  and  fine 


a  Mon.  U.  S.  Geol.  Survey,  vol.  36,  1899,  pp.  398-405. 


i-lbid.,  pp.  406-411. 


40  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

exposures,  in  the  vicinity  of  West  Vulcan.  It  is  threefold,  comprising  a 
series  of  quartzites  and  fragmental  ores  at  the  base,  called  the  Traders 
member;  following  these  in  upward  succession,  a  series  of  slates  known  as 
the  Brier  slates;  and  above  these,  a  set  of  ore  beds,  jaspilites,  and  quartzites, 
which  has  been  called  the  Curry  member,  the  names  in  each  case  being 
taken  from  the  names  of  the  mines  near  which  the  respective  series  is  best 
exposed. 

The  Hanbury  slates  are  thus  named  because  in  the  vicinity  of  Lake 
Hanbury  this  formation  is  better  exposed  than  anywhere  else  in  the  district. 

References  to  Marquette  monograph. — In  the  following  pages  references 
will  be  made  repeatedly  to  the  monograph  on  the  Marquette  district,  espe- 
cially in  connection  with  the  discussion  of  the  Archean  rocks.  These  are 
so  nearly  like  the  corresponding  rocks  in  the  Marquette  district  that  a 
minute  description  of  them  would  be  little  more  than  a  repetition  of  what 
has  already  been  recorded  in  the  account  of  the  Marquette  Basement 
Complex.  In  order  to  avoid  this  unnecessary  repetition,  only  brief  descrip- 
tions of  these  rocks  will  be  given.  Those  who  may  be  interested  in  their 
petrography  are  referred  to  the  chapter  on  the  Basement  Complex  in  the 
Marqviette  monograph,"  and  to  Dr.  Williams's  bulletin ''  on  the  greenstone- 
schist  areas  of  the  Menominee  and  Marquette  regions  of  Michigan. 

"Van  Hise,  C.  R.,  and  Bayley,  W.  S.,  The  Marquette  iron-bearing  district  of  Michigan,  including 
a  chapter  on  the  Republic  trough"by  H.  L.  Smyth:  Hon.  U.  S.  Gaol.  Survey,  vol.  28, 1897,  pp.  149-220. 

1)  Williams,  G.  H.,  The  greenstone-schist  areas  of  the  Menominee  and  ISIarquette  regions  of  Michi- 
gan; a  contribution  to  the  subject  of  dynamic  metamorphism  in  eruptive  rocks:  Bull.  U.  S.  Geol. 
Survey  No.  62,  1890. 


CHAPTER    II. 

BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE. 

The  geological  literature  relating  to  the  Menominee  district  is  much 
less  voluminous  than  that  relating  to  the  Marquette  district.  Nearly  all  of 
it  is  concerned  more  particularly  with  the  general  problems  presented  by 
the  district.  Very  little  of  the  work  done  has  been  accomplished  by  geol- 
ogists working  privately.  By  far  the  greater  portion  of  it,  including  all 
that  is  of  the  greatest  value,  is  the  result  of  public  enterprise.  The 
earliest  important  publications  are  those  of  the  United  States  geologists 
who  were  intrusted  with  the  examination  of  the  geological  features  of  the 
"Chippewa  land  district."  After  these  came  the  publications  of  the  Michi- 
gan survey,  followed  by  those  of  the  Wisconsin  survey,  and,  finally,  by 
those  of  the  U.  S.  Geological  Survey.  The  authors  who  have  done  most 
toward  familiarizing  us  with  the  broader  features  of  the  Menominee  geology 
are  J.  W.  Foster,  J.  D.  Whitney,  T.  B.  Brooks,  C.  Rominger,  and  R.  D. 
Irving.  Messrs.  Foster  and  Whitney  first  recorded  the  existence  of  pre- 
Cambrian  rocks  within  the  limits  of  the  district.  Brooks  separated  these 
into  the  Laurentian  and  the  Huronian  groups,  and  published  maps  outlining 
the  Huronian  basin  and  the  distribution  of  the  principal  formations  repre- 
sented in  it.  This  author  and  Rominger  both  give  a  great  many  details 
with  reference  to  the  relations  of  these  formations  to  each  other,  and  both 
worked  out  a  general  theory  of  structure  for  the  bedded  rocks.  Irving- 
busied  himself  principally  with  a  discussion  of  the  relations  of  the  iron- 
bearing  formation  to  the  overlying  and  the  underlying  series. 

Brooks's  map  (PI.  IV)  is  the  only  detailed  one  of  the  district. 
Others  that  have  been  issued  are  mainly  copies  of  this,  except  the  map  of 
C.  E.  Wright,  which  was  constructed  primarily  for  economic  purposes,  and 
which  shows  merely  the  outline  of  the  Huronian  basin  and  the  distribution 
of  the  iron-bearing  and  the  green-schist  formations  within  it. 

41 


42  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

In  the  present  chapter  reference  is  made  to  all  tlie  articles  that  are 
known  to  treat  of  the  district  under  discussion.  These  are  abstracted  in 
each  case,  and  the  conclusions  reached  are  outlined.  A  knowledge  of  the 
contents  of  many  articles  that  treat  of  the  relations  of  the  pre-Cambrian 
formations  to  one  another  in  the  Lake  Superior  region,  but  which  do  not 
refer  specifically  to  the  Menominee  district,  is  of  importance  to  the  correct 
understanding  of  the  history  of  the  discussion  of  the  Menominee  geology, 
but  they  have  been  so  fully  referred  to  in  the  monograph  on  the  Marquette 
district "  that  it  has  not  been  thought  necessary  to  abstract  them  a  second 
time. 

The  ai-rangement  of  the  abstracts  is  chronological,  the  dates  of 
publication  of  the  original  articles  being  regarded  as  the  times  when  they 
were  first  made  public.  This  method  of  arrangement  is  unfair  to  a  few 
authors,  notably  to  Dr.  Romiuger,  a  portion  of  whose  work  was  first 
published,  through  no  fault  of  his  own,  years  after  it  was  completed,  and 
to  certain  others  of  the  official  geologists ;  but  it  is  the  only  method  that 
is  practicable,  since  it  is  impossible  in  most  cases  to  learn  when  the  various 
articles  left  the  hands  of  their  authors. 

The  very  first  information  given  us  concerning  the  district  now  under 
discussion  was  imparted  through  documents  of  Congress.  The  first  author 
who  left  a  record  of  his  obsei'vations  in  the  Menominee  country  was 
George  N.  Sanders.  Following  his  report  came  the  reports  of  the  other 
early  United  States  geologists  in  rapid  succession.  Then  ensued  a  period 
during  which  little  new  work  was  done.  In  1877  the  discovery  of  ore 
at  the  Breen  mine  called  renewed  attention  to  the  district.  This  is  shown 
in  the  excellent  reports  of  the  Michigan  and  Wisconsin  geologists,  published 
between  the  years  1872  and  1881.  The  investigations  begun  by  these 
surveys  were  continued  without  interruption  by  the  United  States  Geolog- 
ical Survey,  but  in  the  Government  survey  the  Menominee  geology  was 
studied  as  a  portion  of  the  broader  problems  relating  to  the  entire  Lake 
Superior  region  prior  to  the  inauguration  of  the  work  on  which  the  present 
volume  is  based. 

a  Van  Hise  C.  R.,  and  Bayley,  W.  S.,  The  Marquette  iron-bearing  district  of  Michigan,  inckiding 
a  chapter  on  the  Republic  trough,  by  H.  L.  Smyth:  Men.  U.  S.  Geol.  Survey,  vol.  28,  1897.  (See 
Chapter  I,  Geological  explorations  and  literature,  pp.  5-148.) 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  43 

1845. 

Sanders,  George  N.  Report  to  J.  J.  Abert:  Sen.  Docs.,  2d  sess.  28th  Cong., 
18^14-45,  vol.  7,  No.  117,  pp.  3-9. 

The  first  known  reference  to  the  Menominee  district  is  found  in  the 
report  of  George  N.  Sanders,  who  made  an  examination  of  the  country  along 
the  Menominee  River  with  a  view  to  determine  the  feasibiHty  of  con- 
structing a  road  from  Grreen  Bay  on  Lake  Michigan  to  Copper  Harbor  on 
Lake  Superior.  In  this  report  we  find  described  the  general  features  of  the 
country  traversed.  The  report  is  topographical  rather  than  geological; 
nevertheless,  the  author  refers  to  various  veins  of  spar  met  with  in  his 
travels. 

Sanders,  George  N.  Report  to  J.  Stockton:  Sen  Docs.,  2d  sess.  28th  Cong., 
1844-45,  vol.  11,  No.  175,  pp.  8-14. 

This  report  is  a  reprint  of  the  preceding  one. 

18-49. 

Foster,  J.  W.  Report  to  Dr.  C.  T.  Jackson:  Sen.  Docs.,  2d  sess.  30th  Cong., 
1848-49,  vol.  2,  No.  2,  pp.  159-163.     Dated  Sept.  28,  1S48. 

In  this  article  the  author  prints  an  abstract  of  his  report  to  Dr.  Jack- 
son, published  in  full  during  the  succeeding  year.  A  brief  description  of 
Menominee  geology  is  given,  the  reader  being  referred  to  the  full  report 

for  details. 

1850. 

Jackson,  C.  T.  Report  on  the  geological  and  mineralogical  survej^  of  the  min- 
eral lands  in  the  State  of  Michigan,  etc.  Sen.  Docs.,  1st  sess.  31st  Cong.,  1849-50, 
vol.  3,  No.  1,  pp.  371-624.     Dated  Nov.  10,  1849. 

Dr.  Jackson's  report  is  devoted  mainly  to  the  region  immediately  bor- 
dering Lake  Superior.  In  it,  however,  the  author  mentions  having  received 
a  specimen  of  slightly  magnetic  iron  ore  from  the  Menominee  River.  It 
was  given  him  by  Mr.  Barbeau,  of  Sault  Ste.  Marie,  who  had  received  it 
from  an  Indian.  Tlie  ore  was  reported  as  occurring  in  mountainous 
masses  somewhere  between  the  head  of  Keweenaw  Bay  and  the  Menominee 
River.  An  analysis  of  the  ore  yielded  89.70  per  cent  FcsOg;  12.20  per  cent 
siliceous  matter. 

Foster,  J.  "W.  Notes  on  the  geology  and  topograph}'  of  portions  of  the  country 
adjacent  to  Lakes  Superior  and  Michigan  in  the  Chippewa  land  district,  pp.  773-801. 
Dated  May  26,  1849. 


44  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Messrs.  Foster  and  Hill  were  sent  by  Dr.  Jackson  to  make  a  section  from 
L'Anse  to  the  Menominee  River  and  to  search  for  the  iron  mountain  referred 
to  in  the  preceding  article.  These  geologists  report  that  "alternating  beds 
of  hornblende  and  argillaceous  slates "  occur  on  the  Menominee  River  about 
1  mile  below  the  junction  of  the  Brule  and  the  Michigamme.  Near  the 
south  line  of  T.  41  N.,  R.  30  W.,  they  also  report  the  existence  of  a  high 
ridge  of  "argillaceous  slate  containing  amygdules  of  calc  spar."  Between 
this  point  and  the  Upper  Twin  Falls  the  argillaceous  slates  and  chloritic 
slates  largely  predominate.  At  these  falls  and  at  the  Lower  Twin  Falls  they 
present  good  sections.  About  2  miles  southeast  of  the  lower  falls,  near  sec. 
30,  T.  40  N.,  R.  30  W.,  large  beds  of  specular  ore  are  associated  with  talcose 
and  argillaceous  slates.  The  ore  is  similar  to  that  of  the  "iron  mountain," 
which  is  now  identified  as  Republic  Mountain,  in  the  Marquette  range. 
Among'  the  other  rocks  observed  on  what  is  now  known  as  the  Menominee 
ransre  were  ffreat  blocks  of  limestone  in  the  Menominee  River  at  the  mouth 
of  the  Misskos  (T.  40  N.,  R.  31  W.),  ledges  of  "hornblende"  exposed  on  the 
banks  of  the  stream,  beds  of  talcose  slate  at  the  foot  of  the  Great  Bekuenesec 
Falls  (now  the  Big  Quinnesec  Falls,  in  the  northwest  portion  of  T.  39  N., 
R.  30  W.),  a  similar  bed  at  the  foot  of  the  Little  Bekuenesec  Falls,  and  a 
third  bed  of  the  same  character  at  the  foot  of  the  Sturgeon  Falls.  At  the 
latter  place  the  slates  are  "wedged  out  between  walls  of  sienite."  At  Chip- 
pewa Island  the  slates  again  occur.  Here  the  authors  constructed  a  section 
with  drift  on  top,  followed  beneath  by  nearly  horizontal  sandstone,  dark- 
colored  basalt,  and  argillaceous  and  talcose  slates.  The  sandstone  rests 
upon  the  upturned  edges  of  the  slate.  Since  its  deposition  the  former  rock 
is  said  to  have  suffered  no  great  alteration  or  disturbance,  whereas  the 
slates  on  which  it  rests  are  contorted  and  altered  by  the  protrusion  of 
igneous  rocks. 

The  iron  ores  referred  to  are  reported  to  "bear  upon  their  surfaces 
strong  marks  of  their  mechanical  origin."     The  report  continues: 

They  are  regularly  stx-atified,  *  *  *  so  that  a  specimen,  on  its  cross  fracture, 
resembles  ribbon -jasper.  The  lines  of  stratification  can  readily  be  distinguished  from 
those  of  lamination.  Like  the  slates,  thej'  are  often  found  contorted  and  wrinkled, 
and  the  same  facts  could  be  advanced  in  both  cases  to  prove  their  common  origin 
[p.  779]. 

This  statement  sounds  strange  in  view  of  the  author's  later  attempt,  in 
conjunction  with  Whitney,  to  show  that  similar  ores  in  the  Marquette 
district  are  eruptive  in  origin. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  45 

In  the  systematic  description  of  the  rocks  met  with  in  the  journey  we 
find  that  a  range  of  rock,  supposed  to  be  granite,  was  discovered  running 
parallel  to  the  Menominee  River,  in  Tps.  39  and  40  N.,  Rs.  30  and  31  W., 
and  crossing-  the  river  at  Great  Bekuenesec  Falls.  On  both  sides  of  this 
range  igneous  hornblende  rocks  were  found. 

1851. 
Foster,  J.  W.,  and  Whitney,  J.  D.     On  the  age  of  the  sandstone  of  Lake 
Superior,  with  a  description  of  the  phenomena  of  tlie  association  of  igneous  i-ocks: 
Proc.  Am.  Assoc.  Adv.  Sci.,  Fifth  Meeting,  pp.  23-38.     1851. 

In  the  course  of  a  genei-al  description  of  the  Lake  Superior  sandstone 
the  authors  state  that  the  belt  of  this  rock  is  14  miles  wide  where  it  crosses 
the  Menominee,  that  it  has  a  gentle  dip  to  the  southeast,  not  exceeding 
3°,  corresponding  with  the  slope  of  the  country,  and  that  in  the  bed  of  the 
river  it  rests  on  vertical  edges  of  slate  rocks  and  of  compact  and  igneous 
rocks  intercalated  with  them. 

Foster,  J.  W.,  and  Whitney,  J.  D.  Report  on  the  geology  of  the  Lake 
Superior  land  district,  pt.  2,  the  iron  region,  together  with  the  genei-al  geology. 
Dated  Nov.  12,  1851.  Sen.  Docs.,  special  sess.  32d  Cong.,  1851,  vol.  3.  No.  -i. 
xvi,  406  pp.,  with  map. 

In  the  general  portion  of  this  report  the  statements  made  to  Dr.  Jack- 
son by  the  senior  autlior  with  reference  to  his  observations  on  the  Menomi- 
nee River  are  repeated.  In  addition  it  is  stated  that  above  the  Big 
Quinnesec  Falls  and  just  above  the  lower  falls  the  rocks  consist  of  serpen- 
tine, and  that  at  the  head  of  the  upper  falls  there  is  a  protrusion  of  a  rock 
like  protogine,  "  composed  of  feldspar,  talc,  and  quartz.  *  *  *  Occasion- 
ally hornblende  replaces  the  talc,  when  it  [the  rock]  passes  into  a  well- 
characterized  syenite"  (p.  25).  Slates  are  mentioned  as  occurring  between 
the  Little  Quinnesec  Falls  and  Sandy  Portage,  and  serpentine  between  the 
latter  place  and  Sturgeon  Falls.  On  the  portage  a  ridge  was  crossed  in 
which  the  rock  has  the  external  character  of  granite,  but  the  mineralogical 
composition  of  protogine.  Slates  and  dark-green  igneous  rocks  alternate 
as  the  Menominee  is  descended,  the  gradations  between  the  igneous  rocks 
being  so  numerous  as  to  prevent  their  proper  classification.  At  soine  dis- 
tance below  the  portage  are  basaltic  and  other  crystalline  greenstones  which 
at  Chippewa  Island  are  declared  to  be  in  contact  with  talcose  slates.  Near 
the  south  end  of  the  island  the  slates  are  described  as  being  porphyritic 


46 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 


with  red  phenocrysts,  and  with  them  are  said  to  be  associated  large  masses 
of  serpentine. 

After  describing  the  rocks  occurring  along  the  Menomi- 
nee the  authors  give  a  general  account  of  the  topog-raphical 
features  of  the  Menominee  Valley,  and  describe  a  geological 
section  (see  fig.  1)  across  the  valley  from  sec.  35,  T.  42  N., 
R.  30  W.,  to  a  point  near  the  Little  Quinnesec  Falls,  in  sec. 
14,  T.  39  N.,  R.  30  W.  The  description  is  taken  from  the 
notes  of  Charles  Whittlesey.  The  quartz  shown  in  the  sec- 
tion is  said  to  pass  into  hornblende-slate,  and  to  the  north 
into  gneissoid  rocks. 

A  large  number  of  observations  were  made  on  the  rocks 
occurring  north  of  the  river,  some  of  which  are  of  interest. 
On  the  north  side  of  Lake  Fumfee  is  a  sharp  and  elevated 
ridge  whose  top  consists  of  Potsdam  and  Calciferous  sand- 
stone resting  undisturbed  on  the  Azoic  rocks  beneath.  In 
sees.  34  and  35,  T.  40  N.,  R.  30  W.,  is  a  compact  marble 
belonging  with  the  Azoic,  and  in  sec.  30  of  the  same  town 
is  a  "conspicuous  iron  mountain."  Iron  ores  were  also  noted 
in  a  ridge  south  of  Antoines  Lake,  in  the  southern  portion 
of  T.  40  N.,  R.  30  W.  These  are  believed  to  be  the  south- 
ernmost ores  in  the  district.  They  are  specular  in  structure 
and  are  of  a  bluish-black  color.  Between  sees.  28  and  29,  in 
f  «-  a  T.  40  N.,  R.  28  AV.,  is  a  great  deposit  of  ore  containing  from 
^    ill   63  to  68  per  cent  of  iron. 

IQ     ^     -*! 

S  .  'f.  The   series   to  which    the   ores,   schists,  limestone,  and 

a.|i.S   quartz  rocks  belong  occupies  a  belt  whose  broadest  expan- 
ds I   sion  is  not  less  than  80  miles  in  width.     The  rocks  compris- 
nig   the    series  are   supposed    to  be    flexed    and    folded,   as 
measurement  across  their  upturned  edges  would  give  a  thick- 
I  ness  for  the  series,  providing  it  is  assumed  to  be  unfolded, 
^"Z'^   too  o-reat  to  be  reg-arded  for  an  instant  as  correct.     The  entire 

"d  o  "a 

Igl  series  is  considered  to  be  metamorphic,  even  to  the  compact 
I'll   "hornblende,"  which  resembles  an  ig'ueous  rock.     Between 
^~^:  the  granite  that  iinderlies  them  and  the  Sihman  sandstones 
^         that  overlie  them  the  rocks  of  the  series — 
throughout  their  whole  extent     *     *     *     are  more  or  less  metamorphosed,  pre- 


a " 

to  f^ 


w   1^ 

GO    3 


O 

&4    CO 

a   (-■ 

<;§ 

s  s 

^  "  6 
.a  <u  c 
"£  ■»  £ 

O    G    X 


^  ^  ^ 

H)    C    qJ 

2-2g 

as  g 


^    O     OJ 


=>  g  c 
c-3  ." 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  47 

sentin^  a  series  of  gradations  represented  at  one  extreme  by  crystalline  gneiss  and 
compact  hornblende  and  at  the  other  by  bedded  limestone  and  ripple-marked  quartz. 
To  the  presence  of  granitic  and  ti'appean  rocks  this  transformation  is,  in  a  great 
degree,  to  be  attributed.  Much  of  the  compact  hornblende  presents  the  external 
characters  of  an  igneous  product;  but,  since  it  is  found  to  occupj^  an  almost  invariable 
relation  to  the  granite  axes — flanking  their  slopes— and  to  assume  a  fissile  structure 
as  it  recedes  from  the  lines  of  igneous  outburst,  we  can  not  but  regard  it  as  the  more 
highly  metamorphosed  portions  of  the  dark-green  chlorite-slates.  This  compact 
hornblende  is  not  to  be  confounded  with  those  lenticular-shaped  masses  observed  in 
the  slates  which,  we  doubt  not,  are  trappean  in  their  nature. 

We  have  seen  that  those  igneous  causes  which  produced  numerous  axes  of  eleva- 
tion, and  folded  the  strata  into  a  series  of  flexures,  had  ceased  to  operate  before  the 
deposition  of  the  Silurian  groups,  since  they  are  found  to  repose  in  a  nearlj^  hori- 
zontal position  upon  the  upturned  edges  of  the  slates,  or  to  occupy  the  sinuosities  in 
the  granite,  nowhere  exhibiting  traces  of  metamoi-phism  or  derangement  of  the 
strata. 

*  *  *  From  the  local  details  above  given,  it  will  be  seen  that  the  igneous 
rocks  of  the  Azoic  period,  though  crystalline,  compact,  and  occasionally  porphj'ritic 
in  their  texture,  are  never  amygdaloidal  (like  the  traps  on  Keweenaw  Point),  and 
hence  we  infer  that  they  were  pi'oduced  under  widely  difl^erent  conditions.  The  lat- 
ter may  have  been  consolidated  beneath  the  pressui-e  of  a  great  ocean,  while  from 
the  former  a  greater  part  of  this  pressure  may  have  been  removed;  or  it  may  be  that 
both  were,  in  the  first  instance,  equally  vesicular,  but  that  the  latter  assumed  a  crys- 
talline or  compact  sti-ucture  from  long-continued  exposure  to  heat,  under  immense 
pressure.  All  the  phenomena  would  seena  to  indicate  that  the  eruption  of  the  trap- 
pean rocks  of  this  period  took  place  beneath  an  ocean  of  great  depth;  or,  at  least 
under  conditions  widely  different  from  those  which  prevailed  during  the  formation 
of  the  trappean  belts  of  Keweenaw  Point  and  Isle  Royale  [p.  32]. 

After  making  some  general  remarks  upon  the  necessity  of  regarding 
the  rocks  below  the  base  of  the  Silurian  as  composing  a  great  system,  which 
they  call  the  Azoic,  the  authors  proceed  to  describe  each  rock  in  detail  and 
to  note  its  occurrence  in  the  region  examined.  They  repeat  many  of  the 
statements  above  referred  to,  and  theorize  as  to  the  origin  and  the  relative 
ages  of  the  different  rocks.  Their  conclusions  with  respect  to  the  age 
of  the  Menominee  rocks  are  not  essentially  different  from  those  reached 
in  the  discussion  of  the  Marquette  rocks — results  that  have  been  freely 
described  in  the  Marquette  monograph."  The  most  important  of  these  con- 
clusions relates  to  the  igneous  origin  of  the  iron  ore,  which  in  the  previous 

a  Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897. 


48 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


year  the  senior  author  had  argued  to  be  sedimentary.  (Cf.  p.  44.)  Two 
other  igneous  rocks  are  especially  noted;  one  is  a  compact,  dark,  horn- 
blendic  rock,  the  other  a  light-colored  rock  resembling  a  member  of  the 
granite  family,  and  designated  a  "feldstone." 


^      =  Iron 
»-"  =  Beds  of  marble 
C.S.=  Crystalline  schists 
P     =  Potsdam  sandstone 
CALr  Calciferous  sandstone 


;   Tragpean  rocks 


'"!x.'JM-   Granite 


Chippewa  Island  (Mw. 


Fig.  2.— Portion  of  the  geological  map  of  the  Lake  Superior  land  district  in  the  State  of  Michigan.    After  Foster  and 
Whitney,  1851.    The  squares  are  toiTnships,  each  embracing  about  31;  square  miles. 

The  map  which  accompanies  the  report  is  intended  to  show  approxi- 
mately the  distribution  of  the  Azoic,  the  Paleozoic,  and  the  igneous  rocks. 
That  portion  of  it  wliich  relates  to  the  Menominee  district  is  here  reproduced 
without  colors  as  fig.  2. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  49 

1855. 

Foster,  J.  W.  Catalogue  of  rocks,  minerals,  etc.,  collected  by  J.  W.  Foster: 
Ninth  Ann.  Rept.  Smithsonian  Institution,  pp.  384:-386.     1855. 

As  its  title  indicates,  this  article  is  simply  a  catalogue  of  specimens. 

1860. 

Whittlesey,  Charles.  On  the  origin  of  the  Azoic  rocks  of  Michigan  and 
Wisconsin:  Proc.  Am.  Assoc.  Adv.  Sci. ,  Thirteenth  Meeting,  pp.  301-308.     1860. 

In  a  somewhat  general  article  on  the  "Azoic"  rocks  of  the  Upper 
Peninsula  of  Michigan,  the  author  records  the  results  of  analyses  of  15 
rocks  collected  mainly  from  the  Menominee  drainage  basin.  By  compari- 
son of  these  analyses  with  those  of  the  Laurentian  rocks  of  Canada,  the 
conclusion  is  reached  that  the  Menominee  "metamorphic  rocks,"  including 
the  slates,  etc.,  must  be  of  a  different  age  from  the  sediments  which  yielded 
the  Laurentian  rocks,  if  these  are  really  metamorphic.  The  author,  how- 
ever, is  inclined  to  doubt  their  metamorphic  origin. 

Igneous  rocks  are  described  as  being  in  contact  with  Potsdam  sandstone 
in  the  Menominee  district,  and  the  sandstone  is  said  to  have  been  metamor- 
phosed at  the  contact.  The  agent  producing  the  change  is  nevertheless 
thought  not  to  be  heat.  It  appears  that  the  author  would  regard  the 
"metamorphic  rocks"  associated  with  the  iron  ores  as  igneous. 

1861. 

WiNCHELL,  A.  First  biennial  report  of  the  progress  of  the  geological  survey 
of  Michigan,  etc.     Lansing,  339  pages.     1861. 

In  this  report  the  only  allusion  to  the  Menominee  district  is  found  in 
the  statement  that  "On  the  State  boundary  the  Azoic  belt  stretches  from 
beyond  Lac  Vieux  Desert  to  Chippewa  Island,  in  the  Menominee  River" 
(p.  49).  The  rocks  of  the  system  are  declared  to  be  talcose,  chloritic,  and 
siliceous  slates,  quartz,  and  beds  of  marble. 

1868. 

Credner,  H.  Die  Gliederung  der  eozoischen  (vorsilurischen)  Formationsgruppe 
Nord-Amerikas:  Zeitschr.  f.  die  Gesammten  Naturwissenschaften,  vol.  32,  1868, 
pp.  353-405,  and  Habilitationschrift  mit  Genehmigung  der  phil.  Fak.  der  Univ. 
Leipzig,  Halle.     1869. 

In  connection  with  a  general  discussion  of  the  pre-Silurian  rocks  of 

MON  XLVI — 04 4 


50  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

North  America,  wliich  are  divided  into  the  Laureutian  and  the  Huronian 
systems,  Credner  describes  briefly  the  geology  of  the  Upper  Peninsula  of 
Michigan. 

The  Laurentian  system  of  IMichigan  is  made  to  consist  of  a  series  of 
gneisses,  mica-schists,  hornblende-schists,  granites,  and  syenites,  with  a  total 
thickness  of  over  20,000  feet.  These  I'ocks  occur  with  many  different 
variations  of  mineralogical  composition,  chloritic  and  talcose  varieties  being 
especially  abundant.  They  all  show  their  sedimentary  origin  in  their 
present  structure.  Besides,  at  the  Falls  of  the  Sturgeon  River  there  are 
typical  conglomerates  interbedded  with  micaceous  and  hornblendic  rocks. 
At  this  point  the  author  observed,  in  the_  midst  of  the  gneiss  series,  several 
hundred  feet  of  a  complex  consisting  of  thin-bedded  talcose  and  sandj- 
ripple  marked  schists,  a  thin  layer  of  protogine-gneiss,  and  three  beds  of 
conglomerate,  each  30  feet  in  thickness.  These  conglomerates  contain 
pebbles  of  gneiss,  granite,  and  quartzite,  varying  in  size  from  that  of  a 
hazelnut  to  that  of  one's  fist,  embedded  in  a  talcose  sandy  grouudmass. 
The  conglomerate  is  described  as  conformably  overlain  by  gneiss. 

No  eruptive  rocks  were  discovered  in  the  Laurentian  of  Michigan 
older  than  the  coarse-grained  and  porphyritic  granite  that  intrudes  the 
gneiss. 

The  Huronian  series  surrounds  the  Laurentian  rocks  and  lies  upon 
them  unconformably.  It  is  characterized  as  a  series  of  sediments  interme- 
diate in  age  between  the  Laurentian  rocks  below  and  the  Silurian  series 
above.  It  consists  of  a  regular  succession  of  quartzites,  limestone,  iron 
ores,  chloritic  and  clay  slates,  and  talc-schists,  with  a  thickness  of  18,000 
feet,  and,  interlaminated  with  them,  beds  of  diorite  and  aphanite.  The 
series  forms  a  major  syncline,  with  a  minor  syncline  extending  into  the 
embayments  along  the  edge  of  the  Laurentian  areas. 

In  tliat  portion  of  the  Menominee  district  where  the  Huronian  system 
is  most  regularly  developed,  this  system  comprises,  in  order,  beginning 
with  the  oldest,  2,000  feet  of  quartzite;  2,000  feet  of  white  or  red  lime- 
stone; 700  feet  of  schistose  hematite,  varying  in  composition  from  a  ferru- 
ginous quartzite  to  a  granular  hematite;  1,200  feet  of  chlorite-schists ;  8,000 
feet  of  gray  clay  slates,  interlaminated  with  layers  of  granular  quartzite; 
1,200  feet  of  chlorite-schists;  2,000  feet  of  coarse  diorite;  and  a  series  of 
talcose  clay  slates  and  quartzose  talc-schists. 

The  limestone  contains  thin  layers  of  siHceous  clay  slate,  bands  of 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE. 


51 


quartzite,  and  occasional  inclusions  of  tremolite.     On  the  south  shore  of 

Lake  Antoine  beds  of  coarse  calcareous  sandstone  and  of  a  conglomerate 

made  up  of  limestone  fragments  in  a  quartzose  groundmass  are  interlam- 

inated  with  the  limestone  beds.     In  the  upper  horizon  of  the  upper  chlorite- 

schists  are  about  100  feet  of  diorites,  and  in  certain  places  about  100  feet 

of  talc-schists.     The  Haronian   series,  like   the   Laurentian,   is   devoid  of 

eruptives. 

1869. 

Ceedner,  H.  Die  vorsilurischen  Gebilde  der  "oberen  Halbinsel  von  Michigan" 
in  Nord-Araerika:  Zeitschr.  Deutsch.  geol.  Ges.,  vol.  21,  pp.  516-554.  Map  and 
four  plates  of  sections.     1869. 

In  a  fuller  account  of  the  pre-Silurian  geology  of  the  Upper  Penin- 
sula of  Michigan  Credner  discusses  the  details  upon  which  the  conclusions 
expressed  in  his  former  paper  (pp.  49-51)  are  based. 


Qiiarzit 


Gnei^. 


Cchiefer  ti.  cunglomerac 


Giieisse 


Flc.  3.— Geological  section  along  the  Falls  of  the  Sturgeon  River.     After  H.  Credner,  1869. 

The  Laurentian  gneisses  and  schists  are  reported  to  exist  as  islands 
projecting  through  the  Huronian  sediments.  The  most  important  Lauren- 
tian rocks  are  mica-gneisses,  hornblende-gneisses,  hornblende-schists,  and 
granites,  with  a  measured  thickness  of  about  10,000  feet  at  the  Falls  of  the 
Sturgeon  River.  Here  the  succession,  beginning  at  the  north,  is  as  follows 
(see  fig.  3): 

(a)  A  great  thickness  of  fine-grained,  micaceous  gray  gneiss,  interbanded  with  coarse-grained, 

feldspathic,  red  gneiss,  and  a  few  beds  of  hornblende-gneiss  and  liornblende-schist. 

(b)  Chlorite-gneiss,  with  streaks  of  chlorite-schist. 

(c)  Talc  (protogine) -gneiss,  through  loss  of  talc  passing  into — 
{d)  Chlorite-gneiss  containing  bands  of  chlorite-schist. 

(e)  Fine-grained  talc-gneiss,  inclosing  a  mass  of  granular  magnetite  and  hematite  one-half 
foot  in  diameter. 

(/)  Fine-grained  mottled  schists  ( ' '  Fleekschiefern "  ) ,  composed  of  fine  plates  of  talc  and  mica 
and  very  small  grains  of  sand  and  of  feldspar.  In  this  are  lenticular  masses  or  thin  bands 
of  pure  feldspar  or  of  flne-grained  talc-gneiss.  The  schist  is  thin  bedded,  and  its  bed- 
ding surfaces  are  marked  by  ripple  marks.  It  occurs  in  four  zones  measuring  from  8 
feet  to  40  feet  in  thickness.     Between  these  are — 

(g)  Three  beds  of  conglomerate,  15-.30  feet  thick,  composed  of  a  matrix  similar  to  the  "Fleek- 
schiefern," filled  with  sharp-edged  and  rounded  fragments  of  granite,  gneiss,  and  quartz, 
varying  in  size  between  a  hazelnut  and  a  man's  fist.  Beds  (/)  and  {g)  dip  vertically  or 
steeply  to  the  south. 


52 


THE  MENOMI^JEE  IRON-BEARING  DISTRICT. 


'7 J-  ^u^  \ 


Obsei'vations  made  a  mile  farther  west  show  that  these  conglomerates 
are  followed  to  the  south  by — 

(V)  Gneiss-granite,  and — 

(t)  Fine-grained  hornblende  rock. 

After  comparing  this  section  with  several  other  sec- 
tions observed  farther  north,  the  author  summarizes  con- 
cerning the  Laurentian  system  as  follows: 

It  con.sists  of  predominating  mica-gneisses  in  all  possible 
varieties  that  may  be  formed  bj'  the  variations  in  structure  and  in 
the  proportions  of  constituents  present,  of  hornblende-gneisses 
and  hornblende-schists  interbedded  with  these,  and  of  chlorite- 
gneisses  and  chlorite-schists  associated  with  zones  of  granite, 
sj-enite,  and  chlorite-granite.  These  constitute  the  surface  rocks 
over  extensive  areas,  strike  with  great  regularity  east  and  west, 
usually  dip  vertically,  are  here  and  there  contorted,  and  are 
intruded  by  3'ounger  granite. 

Less  broadly  distributed  are  two  series  of  talcose  and  chloritic 
forms.  One  series  is  composed  of  talc-gneiss,  talcose  mottled 
schists  ("Fleckschiefern"),  and  conglomerates,  with  a  sandy 
talcose  groundmass.  The  other  series  consists  of  talc-chlorite- 
schists,  with  zones  of  crystalline,  dolomitic  limestone,  chlorite- 
gneiss,  chloritic  hornblende  rock,  chlorite-schists  with  quartz  peb- 
bles, and  foliated  talc-gneiss.  Between  the  equivalents  of  these  as 
described  in  Canada  are  three  limestone  zones,  of  which  the  upper- 
most contains  the  Eozoon  canadense.  In  the  Laurentian  lime- 
stones of  the  Upper  Peninsula  of  Michigan  I  have  not  been  so 
fortunate  as  to  discover  this  fossil  [pp.  525-526.] 

The  Laurentian  areas  are  surrounded  by  a  schist 
system  composed  of  quartzite,  limestones,  iron-bearing 
rocks,  and  crystalline  schists.  Beginning  at  the  bottom, 
the  system  consists  of  the  following  (see  lig.  4) : 

(a)  Dense,  glassy,  or  sugary  quartzite,  thick  bedded  or  thinly  lami- 
nated, and  possessing  coatings  of  yellow  mica  in  its  foliation 
joints.     Thickness,  about  3,000  feet. 
(6)  Crystalline  dolomitic  limestone.     Rarely  pure.     Generally  impure 
through  admixture  of  silica.     Its  texture  varies  between  coarse 
grained  and  very  fine  grained.     Its  color  may  be  yellow,  red. 
Its  bedding  is  thick  or  thin,  anil  the  planes   between  the  layers  are 
Sometimes  there  are  interpolated  between  them  thin  beds  of  argillaceous 
Quartz  veins  penetrate  the  dolomite  in  thin  and 

The 


1^  ^SllOUtOlt^Jf^ 


brown,  or  white. 

sharply  marked. 

chlorite-schist  and  siliceous  clay  slate. 

thick  seams,  which  are  more  abundant  in  the  upper  portions  than  in  the  lower  parts. 

variation  in  the  amount  of  quartz  present  is  exhibited  in  the  topographic  differences  noted. 

Occasionally  the  dolomite  contains  tremolite.     Thickness,  3,.500feet. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  53 

(c)  Hematite  rock.     This  varies  from  a  ferruginous  quartzite  or  a  ferruginous  clay  slate  to  a 

pure  steel-gray  dense  or  granular  hematite  (Rotheiseustein).  It  is  thinly  schistose  to 
thick  bedded,  but  usually  occurs  as  a  series  of  beds  about  an  inch  thick,  in  which  sili- 
ceous and  iron-rich  bands  alternate.  In  a  few  zones  the  jasper  layers  are  entirely  lack- 
ing and  beds  of  iron  ore  30  feet  thick  replace  them.  The  ore  is  free  from  phosphorus 
and  sulphur,  but  it  contains  everywhere  traces  of  magnetite.  Thickness  of  the  group, 
600  to  1,000  feet.  The  cjuartzite  underlying  the  dolomite  is  also  ferruginous  in  places  in 
its  upper  horizons  and  is  consequently  colored  red.  At  several  points  the  ferruginous 
material  is  thought  to  be  sufficiently  concentrated  to  constitute  ore  bodies. 

(d)  Chlorite-schist,  with  spots  and  thin  stains  of  red,  ferruginous  clay.     Interlaminated  with 

the  schist  are  layers  of  quartz  3-4  feet  thick.     Thickness,  probablj-  1,000-1, .500  feet. 
(«)   Clay  slate,  gray,  thinly  laminated  and  rusty  brown  on  its  schist  planes;  or  blue,  black, 

and  very  finely  schistose.     In  the  midst  of  the  slate  is  a  150-foot  bed  of  quartzite, 

which  is  very  hard,  granular,  bluish  gray,  and  is  penetrated  by  veins  of  white  glassy 

quartz  and  red  orthoclase.     Thickness,  8,500  feet. 
(/)  Dark-green  chlorite-schiist,  often  argillaceous.     Thickness,  1,200-1,400  feet.     In  its  upper 

horizons  fine-grained  and   coarse-grained  diorites  in  beds  varying  from  ten  to  several 

hundred  feet  are  associated  with  the  schist. 
(g)  Feldspathic  talc-schist,  light  yellow  or  light  brown  in  color.     Thickness,  30  feet. 
(h)  Greenish-gray  talc-schist,  flecked  with  emerald-green  spots  and  containing  rounded  quartz 

grains.     Associated   with    the   schist  are   very  thin   lenticular  laminae  of  crystalline 

dolomite.     Thickness,  30  feet, 
(i)  Flesh-colored  feldspathic  talc-schist,  containing  lenticular  grains  of  quartz.     Thickness,  40 

feet. 
(k)  Fine-grained  rock  consisting  of  a  feldspathic  groundmass,  containing  plates  of  talc,  small 

reddish-brown  orthoclase,  and  gray  quartz  grains.     Thickness,  50  feet. 
(1)  Diorite  rock  series,  2,300  feet  thick. 
(»rt)  Talcose  clay  slate  and  quartzose  talc-schist,  1,500  feet  thick.     This  series  is  the  yoimgest 

in  the  Upper  Peninsula  of  Michigan.     Farther  south  in  AVisconsin  the  same  rock  series 

occurs,  but  here  it  dips  to  the  north,  forming  a  basin  with  the  northern  schists. 

The  beds  (ff),  [It),  (i),  and  (A)  seem  to  possess  only  a  slight  horizontal 
extension.  They  are  local  in  their  development.  They  are  most  fully 
developed  at  the  Big  Quinnesec  Falls,  but  rapidly  wedge  out  on  botli 
sides  along  their  strike.  At  the  Little  Quinnesec  Falls  a  portion  of  the 
talc-schist  series  is  replaced  by  chlorite-schist  and  a  diorite  bed  12  feet 
thick. 

The  lowermost  member  of  the  Huronian,  the  quartzite,  lies  uncou- 
formably  upon  the  gneisses.  The  other  members  of  the  iron-bearing 
series  follow  the  quartzite  conformably.  In  the  neighborhood  of  Lake 
Antoine  they  are  folded  into  two  synclines,  with  limbs  dipping  very  steeply 
toward  the  axes  of  the  folds.  South  of  the  southern  fold  the  entire  iron- 
bearing  series  is  repeated,  with  a  steep  southern  di]),  forming  the  north  side 
of  a  third  syncline  with  its  south  side  in  Wisconsin. 


54 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


Over  the  Hiironian  rocks  in  many  places  lie  patches  of  horizontal 
Potsdam  sandstone  and  Calciferous  sandstone.  Two  sections  showing  the 
relations  of  the  Potsdam  to  the  underlying  rocks  are  given.  The  entire 
district  is  supposed  to  have  been  covered  formerly  with  Paleozoic  sedi- 
ments, as  is  the  district  farther  east  at  the  present  time,  the  patches  on  the 
tops  of  the  hills  being  the  remnants  of  this  covering,  which  have  thus  far 
resisted  the  combined  effect  of  weathering  and  the  action  of  the  ice. 

In  a  few  words,  the  iron-bearing  series  as  developed  in  the  southern  part  of  the 
Upper  Peninsula  of  Michigan  is  characterized  as  follows:   A  conformable  series  of 


Fig. 


-Portion  of  geological  map  of  the  Upper  Peninsula  of  Michigan.    After  H.  Credner,  1869.    The  squares  are  town- 
ships, each  embracing  about  36  square  miles. 


quartzites,  limestone,  hematite,  clay  slates,  chlorite-schists,  and  talc-schists,  the  last 
two  associated  with  beds  of  diorite  and  having  a  total  thickness  of  20,000  feet, 
overlies  unconformablj'  a  gneiss  series,  and  is  in  turn  unconformably  overlain  by 
Silurian  beds.  This  schist  complex  occupies  the  entire  distance  between  gneiss  and 
granite  rims  in  long  narrow  folds.  Organic  remains  have  not  been  discovered 
anywhere  in  the  series  [p.  534]. 

The  Menominee  district  is  thought  to  have  remained  under  water 
longer  than  the  northern  or  Marqixette  district,  since  in  the  former  district 
above  the  quartzite  a  great  thickness  of  rocks  occurs  which  in  the  northern 
district  is  not  represented  at  all. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE. 


55 


The  map  accompanying  the  article  shows  the  general  distribution  of  the 
Archean,  the  Hnronian,  and  the  Paleozoic  formations  in  the  Upper  Pen- 
insula.    That  portion  covering  the  Menominee  district  is  reproduced  in  fig.  5. 

1870. 

Crednek,  H.     Ueber  Nordamerikanische  Schieferporphyi'oide:  Neues  Jahrbuch 
fur  Min.,  etc.,  pp.  970-98-i.    1870. 

At  the  Big  Quinnesec  Falls  of  the  Menominee  River,  in  the  upper  por- 
tion of  the  Huronian  series,  as  defined  by  Credner,  is  a  belt  of  porphyroid 
schists,  about  300  feet  in  thickness,  lying  between  two  beds  of  diabase 
(the  diorite  of  former  articles).  The  schists  comprise  50  feet  of  slightly 
schistose  orthoclase-porphyroid,  10  feet  of  feldspathic  paragonite-schist,  30 
feet  of  orthoclase-paragonite-schist,  15  feet  of  paragonite-schist,  15  feet  of 
calcareous  paragonite-schist,  30  feet  of  schistose  porphyroid,  50  feet  of  cal- 
careous chlorite-schist,  and  100  feet  of  chlorite-schist.  Above  and  below 
this  schist  series  are  diabase  layers,  which  separate  the  porphyroids  from  an 
underlying  series  of  chlorite-schists  and  an  overlying  series  of  siliceous 
talc-schists.  The  petrographical  composition  of  the  porphyroids  is  carefully 
discussed.  All  of  the  acid  members  consist  essentially  of  quartz,  ortho- 
clase,  and  paragonite  in  varying  proportions.  Analyses  of  four  vai'ieties, 
the  first  two  by  Aarland,  the  third  by  Berghandler,  and  the  fourth  by 
Bornemann,  resulted  as  follows: 

Analyses  of  porpkyroid  cmd  schists  from  Big  Quinnesec  JFalls,  Menominee  River. 


Orthoclase- 
porphyroid. 

Felds.  para- 
gonite- 
schist. 

Ortlio.  para- 
gonite- 
schist. 

Paragonite- 
schist. 

SiOj 

66.70 
15.  90 
4.70 
tr. 
tr. 

72.45 
8.85 
6.20 

tr. 

tr. 

76.51 
7.95 

8.88 

tr. 
.32 

tr. 
1.02 
4.38 

75  50 

AI2O3                              

8  60 

Fe,0, 

2  60 

MnO 

CaO 

7  '^0 

MgO 

1  '>0 

KjO 

8.06 
5.50 

9.24 
3.70 

30 

NajO 

3.00 
1  50 

H,0 

Total 

« 100.  80 

« 100. 50 

99.06 

99.90 

"These  totals  are  as  given  in  the  original.     The  correct  footings  are  100.86  and  100.44, 

After  examining  the  theories  proposed  to  account  for  these  and  similar 
rocks,  the  author  concludes  that  they  are  not  eruptives,  nor  are  they  meta- 


56  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

raorpliosed  sediments.     On  the  other  hand  he  regards  them,  together  with 

all  the  other  Huronian  rocks  and  all  the  Laiirentian  series,  as  crystalline 

sediments,  thrown  down  from  the  waters  of  the  pre-Silurian  ocean.     Later 

they  may  have  suffered  some  alteration  tlirough  the  influence  of  mineral 

waters. 

1873. 

Brooks,  T.  B.  Iron-bearing  rocks  (economic):  Geol.  Surv.  Michigan,  Vol.  I, 
part  1.  Chap.  IV,  pp.  157-182.  With  atlas  plates,  three  of  which  relate  to  the 
Menominee  district.     1873. 

At  the  time  Major  Brooks  published  his  report  on  the  Menominee 
district  but  two  mines,  the  Breen  and  the  Ingalls,  had  been  opened,  so  that 
the  author,  in  his  study  of  the  district,  was  compelled  to  rely  for  his  data 
almost  exclusively  upon  surface  exposures.  Many  of  the  facts  he  records 
in  connection  with  the  geology  of  the  district  were  obtained  largely  from  a 
survey  made  by  Messrs.  Pumpelly  and  Credner  for  the  Portage  Lake  and 
Lake  Superior  Ship  Canal  Company. 

In  the  chapters  preliminary  to  the  one  devoted  to  the  Menominee 
district  several  facts  are  incidentally  noted  which  throw  considerable  light 
upon  the  author's  views  concerning  Menominee  geology.  The  hills  in  the 
drainage  basin  of  the  Menominee  River  are  reported  to  be  capped  with 
horizontal  Silurian  sandstone,  which  once  also  probably  filled  the  valleys 
between  them  (p.  68).  In  comparison  with  the  ]\Iarquette  district  the 
Menominee  district  is  simpler  in  its  geological  structure,  and  it  possesses  a 
correspondingl}'  less  varied  topography.  The  elevations  trend  nearly  east 
and  west.  The  south  iron  range  is  the  Menominee  range  proper — the  one 
discussed  in  the  present  monograph.  The  north  range  is  that  now  known 
as  the  Felch  Mountain  or  Metropolitan  range.  Its  geology  was  discussed 
in  the  Crystal  Falls  monograph."  The  southern  range  can  be  traced  15 
miles  in  a  WNW.  direction  through  T.  39  N.,  R.  29  W.,  and  T.  40  N.,  R.  30 
W.  (p.  72).  Its  structure  is  so  simple  that  "whoever  identifies  the  upper 
marble  in  the  Menominee  region  has  a  sure  key  to  the  discovery  of  any  ore 
which  may  exist  in  the  vicinity"  (p.  74).  In  Chapter  IV  of  the  report 
the  general  geology  of  the  district  is  discussed,  many  localities  of  the 
different  rock  types  occun-ing  within  it  are  mentioned,  and  three  structural 
sections  across  the  iron-bearing  series  are  described. 


«Mon.  U.  S.  Geol.  Survey,  vol.  36, 1899. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  57 

The  Menominee  belt  of  ore-bearing  rocks  is  separated  from  the  more 
northerly  belt .  of  similar  rocks  by  a  Avedge-shaped  area  of  granite.  The 
most  easterly  exposure  of  ore  in  the  southern  belt  is  at  the  Breen  mine,  in 
the  north  half  of  the  northwest  quarter,  sec.  22,  T.  39  N.,  R.  28  W.  Travel- 
ing from  this  point  toward  the  west,  following  a  course  running  16° 
north  of  west,  several  other  exposures  of  ore  are  encountered  before  the 
last  ore  in  Michigan  is  met  with  in  the  center  of  the  southeast  quai'ter,  sec. 
25,  T.  40  N.,  R.  31  W.  By  magnetic  observations  the  ore  belt  was  traced 
across  the  Menominee  River  into  Wisconsin,  where  its  probable  continuation 
is  marked  by  outcrops  between  the  Brule  and  the  Pine  rivers.  Immediately 
north  of  this  iron-bearing  belt  is  a  broad  belt  of  impure  marble,  and  north 
of  this,  in  the  Adcinity  of  the  Sturgeon  River,  are  local  magnetic  attractions 
and  a  few  iron-ore  bowlders  that  are  believed  to  mark  the  position  of  a  second 
ore  belt,  which  outcrops  as  a  siliceous  ore  north  of  Lake  Antoine.  North  of 
this  second  ore  belt,  and  underlying  it,  is  an  immense  bed  of  quartzite. 

This  quartzite,  although  believed  to  be  geologically  conformable  with  the  ore 
formations,  is  not  parallel  with  them,  running  more  northwesterly,  and  dividing  in 
T.  40  N.,  R.  30  W.,  into  two  and  perhaps  three  ranges  [p.  159]. 

North  of  the  quartzite  and  underlying  the  whole  series,  which  is 
Huronian  in  age,  are  the  Laurentian  granites,  gneisses,  and  schists. 

South  of  the  southern  belt  is  a  bed  of  chloritic  schist  that  is  well 
exposed  on  the  south  shore  of  Lake  Haubury  and  on  the  Sturgeon  River, 
and  south  of  this  is  a  second  quartzite,  very  different  from  that  to  the 
north.  South  of  the  quartzite  follows  a  broad  exposure  of  argillaceous 
slate  in  a  belt  running  nearly  parallel  to  the  ore  belt.  It  is  exposed  at 
several  points  in  T.  39  N.,  R.  28  W.,  and  in  T.  39  N.,  R.  29  W.  Finally, 
south  of  the  slates, 

is  a  broad,  well-detined  belt  of  chloritic,  hornblendic,  and  dioritic  rocks  running 
parallel  with  the  iron  range,  the  harder  members  of  which  form  the  barrier  rocks  of 
all  the  falls  in  this  part  of  the  Menominee,  and  probably  those  of  Pine  River  in 
Wisconsin  [p.  159]. 

Above  the  iron-bearing  series  is  the  Silurian  sandstone,  which  occurs 
as  the  capping  of  many  of  the  hills  of  the  iron-bearing  area  and  completely 
covers  both  Laurentian  and  Huronian  rocks  a  few  miles  east  of  the  last 
known  exjDOSure  of  ore  at  the  Breen  mine. 


58  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

With  regard  to  the  structure  of  the  district  the  author  declares  that, 
like  their  equivalents  in  the  Marquette  district,  the  Menominee  rocks 
usually  conft)rm  in  strike  with  the  trend  of  the  belts  and  dip  at  high  angles, 
thus  presenting  their  upturned  edges  to  the  observer.  The  conditions  are 
thus  not  favorable  for  working  out  the  structure  of  the  district,  especially 
in  view  of  the  difficulty  in  distinguishing  between  cleavage  and  bedding  in 
the  slates  and  chlorite-schists.  The  north  and  south  ranges  taken  together 
constitute  a  great  east-west  anticline,  of  which  the  Laurentian  area  is  the 
great  backbone  on  and  against  which  the  iron  series  reposes. 

In  order  to  picture  the  structure  two  sections  across  the  district  are 
described,  one  crossing  the  Menominee  River  at  Sturgeon  Falls  in  sec.  27, 
T.  39  N.,  R.  29  W.,  and  the  other  passing  just  east  of  Lake  Antoine. 

The  lowermost  rocks  in  the  first  section  (fig.  6)  are  unmistakably 
Laurentian  (D).  They  comprise  granite,  syenite,  various  gneisses  and 
schists,  and  some  chloritic  and  talcose  slates.     Separating  these  from  the 

Menominee  L.<ilce  Pine  ^^ 

River  ^^' .^~^^_      Hanljurv    ^^"'^NRiver  /        /  ^       ~~- _ 


Fig.  6. — Geological  section  through  Sturgeon  Falls.    After  T.  B.  Brooks,  1873.    Horizontal  scale  given  is  approximate. 
Vertical  scale  is  exaggerated.    For  significance  of  letter-symbols,  see  PI.  III. 

unmistakably  Huronian  sediments  is  a  series  of  soft,  light-gray,  talcose 
slates  underlain  by  four  beds  of  conglomerates,  which  in  turn  are  underlain 
by  two  beds  of  protogine-gneiss,  separated  by  a  bed  of  chlorite-schist. 
These  rocks  the  author  states  are  regarded  by  Pumpelly  and  Credner  as 
Laurentian,  though  he  is  not  certain  that  they  are  of  this  age. 

The  undoubted  Huronian  series  includes,  beginning  with  the  lower- 
most, a  light-gray,  massive  vitreous  quartzite  (1);  a  quartzose  sandstone  and 
conglomerate  (II),  that  may  be  equivalent  to  the  marble  outcropping  in 
sees  24  and  25  in  T.  40  N.,  R.  30  W.;  magnetic  ore  (HI),  whose  existence 
is  indicated  by  bowlders  only;  a  great  development  of  thin-bedded, 
usually  light-gray  marble  (IV),  whose  upper  portions  contain  seams  of 
slate;  the  main  ore-bearing  formation  (V),  consisting  of  siliceous  specular 
slate  ores  corresponding  very  nearly  to  the  flag  ores  of  the  Marquette 
district;  chlorite-schist  (VI);  a  bluish  and  greenish  slate  (^^H),  showing 
indistinctly  a  distorted  bedding  with  prevailing  northerly  dips;  a  bluish- 
gray  quartzite  (VIII),  dipping  north  at  45°-76°;  magnesian  schists  (IX) 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  59 

near  the  Menominee  River;  granular  diorite  (X);  and  magnesian  schists 
and  protogine  (XI).  The  quartzite  may  be  simply  a  local  bed  in  the 
clay-slate  formation.  Marked  contortions  in  both  the  slate  and  the 
quartzite  are  observed,  which  point  unmistakably  to  the  presence  of  a 
great  fold  indicated  in  the  section  as  a  combination  of  an  anticline  with 
a  syncline. 

In  the  second  section  (fig.  7)  the  Huronian  beds  are  arranged  in  the 
same  sequence.  First,  to  the  north  comes  the  quartzite  (I)  in  a  great 
synclinal  fold;  then  marble  (II),  corresponding  to  the  friable  sandstone  in 
the  first  section.  Next  follows  a  bed  of  siliceous  red  iron  ore  resembling 
the  ore  of  formation  V,  but  which  is  probably  the  western  extension  of 
formation  III.  Dr.  Credner  connects  this  bed  with  bed  V,  farther  south,  in 
a  synclinal  fold,  but  the  author  is  inclined  to  regard  it  as  an  independent 
bed  at  a  lower  horizon  than  V.  Above  bed  III  is  the  great  marble 
formation  (IV),  and  then  the  great  iron  formation  (V).  Beds  VI,  VII,  VIII 
of  the  first  section  (fig.  6)  have  no  equivalents  in  the  second  section,  their 


Menominee  R.  te"rraces 

-^ 

1  ifojfsrfa/n^*-...^^^^ 

Lake 

/■" 

\    \         Pine  River 

/e/f/e/f/ 

/  H 

/^ 

/       D 

/ 

/    D 

X&IX         VIII 

0 

VI  r 
1 

VI     V         .,       IV 

2  miles 

III 

I 

'  '  i'^- -''  I  ' 

Fig.  7.— Geological  section  through  Lake  Antoine.    After  T.  B.  Brooks,  1872.    Horizontal  scale  is  approximate.    Vertical 
scale  is  exaggerated.    For  signiticance  of  letter-symbols,  etc..  see  PI.  III. 

places  being  covered  with  drift.  In  the  place  where  formation  VI  should 
occur,  according  to  the  author's  hypothesis  of  the  structure,  Pumpelly 
observed  a  large  ledge  of  marble.  The  existence  of  this  marble  in  this 
place  leads  Brooks  to  suppose  that  there  may  be  folds  in  the  rocks  in  this 
vicinity  not  revealed  by  his  studies.  Formations  IX  and  X  are  the 
chloritic,  hornblendic,  and  dioritic  rocks  exposed  at  the  Big  and  Little 
Quinnesec  Falls. 

The  description  of  the  sections  concludes  the  discussion  of  the  general 
structure  of  the  district.  There  are  several  further  references  to  the  ores, 
exposures  of  rocks,  etc ,  but  detailed  studies  of  them  are  not  recorded. 

PI.  VII  of  the  volume  is  a  magnetic  map  of  T.  40  N.,  R.  30  W., 
showing  two  lines  of  magnetic  disturbance  crossing  the  southern  jjortion 
of  the  township  and  running  in  a  NNW.  direction.  PI.  IV  in  the  atlas 
accompanying  the  report  is  a  geological  map  of  the  district,  exhibiting  the 
author's  theory  of  the  structure.     It  is  reproduced  as  PI.  Ill  of  this  volume. 


60  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

RoMiNGER,  C.     Paleozoic  rocks:  Geol.  Surv.  Michigan,  vol.   1,  part  3,  p.  102. 
1873. 

The  author  introduces  his  work  on  the  Paleozoic  rocks  of  the  Upper 
Peninsula  with  a  few  preliminary  remarks  on  the  general  geology  of 
northern  Michigan.  Only  a  few  of  his  statements  refer  to  the  Menominee 
district. 

The  existence  of  the  upjDer  beds  of  the  Potsdam  sandstone  at  the 
Breen  mine  is  noted.  The  Menominee  limestone  is  thought  "to  be  con- 
nected  with  the  slates  and  quartzite  beds  of  the  upper  division  of  the 
Huronian  series"  (p.  100).  The  rock  occurs  in  thick  layers  of  a  white, 
cream  color  or  of  a  reddish  tint.  It  is  compact,  subcrystalline,  and  verj^ 
hard  In  composition  the  limestone  is  dolomitic,  as  is  shown  from  the 
following  analysis  of  a  specimen  from  the  Sturgeon  River: 

Analysis  of  liTnestone  from  Sturgeon  River. 

Per  cent. 

CaCOs 61-00 

MgCOa ^-t.OO 

Hydrated  oxide  of  Fe  and  JMii 1. 00 

Siliceous  matter 25 

In  many  localities  the  limestone  is  cut  by  a  dense  network  of  coarse 
quartzose  seams.  On  the  Sturgeon  River  the  seams  are  lacking,  but  the 
ledges  are  crossed  in  all  directions  by  fine  fissures. 

Brooks,  T.  B.  ,  and  Julien,  A.  A.  Catalogue  of  the  Michigan  State  collection 
of  the  Huronian  rocks  and  associated  ores:  Geol.  Surv.  Michigan,  vol.  2,  Appendix 
B,  pp.  199-212.     1873. 

In  the  description  of  this  collection  we  find  one  of  a  pyritiferous 
talcose  gneiss  from  the  Falls  of  the  Sturgeon  River,  one  of  a  dolomite  from 
sec.  11,  T.  39  N.,  R.  29  W.;  one  of  a  hematite-schist  from  sec.  11,  T.  39 
N.,  R.  29  W.;  one  of  an  ocliery  hematite  from  the  Breen  mine;  and  one  of 
a  porphyritic  speckled  diorite  from  Sturgeon  Falls  on  the  Menominee. 

Jenney,  F.  B.  Magnetic  analj'ses  and  color  of  powder  of  Marquette  ores: 
Geol.  Surv.  Michigan,  vol.  2,  Appendix  H,  pp.  257-260.    1873. 

This  article  contains  the  results  of  the  determination  of  the  quantity 
of  the  magnetic  and  of  the  nonmagnetic  constituents  in  10  specular  ores 
from  the  Menominee  district. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  61 

1876. 
Brooks,  T.  B.     On  the  youngest  Huronian  rocks  south  of  Lake  Superior  and 
the  age  of  the  copper-bearing  series:  Am.  Jour.  Sci.,  3d  series,  vol.  11,  pp.  206-211. 

1876. 

In  the  summer  of  1874  the  author  and  Professor  Wright  discovered  a 
large  granitic  area  south  of  the  Menominee  River.  On  its  northern  side  it 
is  bounded  by  micaceous  and  hornblendic  schists,  the  former  of  which  are 
penetrated  by  a  few  small  granite  dikes.  These  schists  ai-e  thought  to  cor- 
respond to  the  youngest  member  of  the  Huronian  series  discovered  in  the 
Marquette  district,  viz,  bed  XIX.  The  prevailing  type  of  the  granite  is  a 
medium-  to  coarse-grained  gray  hornblendic  rock  that  is  more  or  less 
gneissic.  The  granite  and  its  associated  schists  bear  such  a  close  resem- 
blance to  the  Laurentian  rocks  exposed  on  the  Sturgeon  River  that  at  first 
they  were  thought  to  be  of  the  same  age  as  these.  A  careful  consideration 
of  the  facts,  however,  inclines  the  author  to  believe  that  the  granites  and 
schists  are  Huronian,  and  from  observations  made  in  the  Peuokee  district, 
he  is  inclined  to  regard  them  as  the  youngest  members  of  this  system.  He 
gives  reasons  for  this  conclusion,  but  they  are  based  almost  exclusively 
upon  observations  made  in  the  Penokee  district. 

In  a  footnote  the  author  calls  attention  to  what  he  considers  an  error 
in  Credner's  correlation  of  the  entire  Marquette  series  with  the  lower 
quartzite  of  the  Menominee  district.  He  thinks  that  Credner  was  led 
astray  by  his  great  overestimate  of  the  thickness  of  the  Menominee  rocks, 
and  by  the  fact  that  he  founded  his  conclusions  largely  on  a  section  of  the 
Marquette  series  made  in  the  neighborhood  of  Negaunee,  where  the  upper 
members  of  the  series  are  entirely  lacking. 

Brooks,  T.  B.  Classified  list  of  the  rocks  observed  in  the  Huronian  series 
south  of  Lake  Supei'ior,  with  remarks  on  their  abundance,  transitions,  and  geo- 
gi'aphical  distribution;  also  a  tabular  presentation  of  the  sequence  of  the  beds,  with 
an  hypothesis  of  equivalency:  Am.  Jour.  Sci.,  3d  series,  vol.  12,  pp.  191^204.     1876. 

The  nomenclature  of  the  rocks  mentioned  in  this  paper  is  based  on  the 
investigations  of  Wichmann,  Wright,  Rutley,  Hunt,  Tornebohm,  and  Wapler. 
The  thickness  of  the  Menominee  beds  is  estimated  at  12,000  feet  or  more. 
The  estimate  of  18,000  given  by  Credner  is  thought  to  be  excessive.  In 
one  instance,  it  is  stated,  this  geologist  mistook  cleavage  for  bedding  and 
thus  "overlooked  at  least  one  synclinal  and  one  anticlinal  fold,  thus  counting 


62  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  same  bed  at  least  three  times"  (p.  195).  In  the  scheme  of  sequence 
and  ft-equency  the  beds  of  the  Marquette  and  of  the  Menominee  series  are 
divided  into  20  formations,  whose  approximate  relative  ages  are  indicated  by 
Roman  numerals.  It  is  unnecessary  to  present  this  scheme  here  as  it  was 
superseded  a  few  years  later  by  a  new  one  which  is  outlined  on  pp.  65-66. 
The  two  do  not  differ  materially  except  in  the  names  of  some  of  the  rocks. 

In  the  description  of  the  table  the  rocks  are  divided  into  (1)  fragmental 
rocks,  exclusive  of  limestone;  (2)  metamorphic  rocks  not  calcareous,  subdi- 
vided into  the  mica-bearing  series,  the  hornblendic  series,  the  felsitic,  epidotic 
and  garnet  rocks,  the  hydrous  magnesian  series,  the  quartzose  rocks,  and 
the  iron  ore  rocks;  (3)  calcareous  rocks;  and  (4)  igneous  rocks,  including  a 
feldspathic  series,  a  hornblendic  series,  a  pyroxenic  series,  and  a  schist 
magnesian  series. 

The  fragmental  rocks  are  conglomerates  and  sandstones.  The  meta- 
morphic rocks  are  granites,  gneiss,  mica-schists,  slates,  syenites,  diorites, 
diabasites  (which  Wichmann  and  Tornebohm  regard  as  eruptives), 
hornblende-scliist,  anthophyllite-schist,  protogine,  talcose  slate,  chloritic 
argillite,  serpentine,  quartzite,  jasper,  magnetite,  hematite,  limonitic  quartz- 
ose ores,  and  a  number  of  other  less  important  types.  The  calcareous  rocks 
embrace  only  limestones  and  dolomites,  and  the  igneous  rocks  only  gi-auites, 
a  few  doleritic,  dioriiic,  and  diabasic  dikes,  massive  and  schistose.  Tlie 
author  states  that  "some  geologists  would  include  here  a  considerable 
portion  of  the  bedded  greenstones  embraced  under  the  metamorphic  rocks" 

(p.  204). 

1879. 

Wright,  Charles  E.  First  Ann.  Rept.  of  the  Commissioner  of  Mineral 
Stati.stics  for  the  State  of  Michigan,  for  1877-S  and  previous  years,  pp.  5-2-i  and 
110-124:.     1879." 

In  the  introduction  to  his  report  the  author  sketches  the  geology  of  the 
Upper  Peninsula.  He  divides  the  pre-Cambrian  rocks  into  Laurentian  and 
Huronian,  placing  all  of  the  iron-bearing-  series  in  the  lower  portion  of  the 

«  The  reports  of  the  Commissioner  of  mineral  statistics  for  the  State  of  Michigan  have  appeared 
annually  since  1879.  They  are  concerned  mainly  with  statistics  and  with  statements  of  the  progress  of 
the  work  under  way  in  the  different  mines.  They  will  be  noticed  in  the  following  pages  only  when 
they  contain  information  bearing  on  the  geology  of  the  ^Menominee  district,  when  this  is  not  plainly  a 
restatement  of  facts  and  opinions  discussed  by  earlier  authorities. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  63 

Huronian.     The  outline  of  the  geology  given  is  not  in  any  respect  different 
froin  that  given  by  Brooks. 

The  only  mines  opened  on  the  Menominee  range  at  this  time  were  the 
Emmett,  Breen,  Vidcan,  Norway,  Cyclops,  and  Quinnesec.  Each  one  of 
these  is  described.  At  the  Emmett  mine  tbere  are  two  kinds  of  ore — a 
soft  specular  variety,  very  low  in  phosphorus,  and  a  brown  one  containing 
1.29  per  cent  of  this  element.  The  latter  lies  beneath  the  former.  At  the 
Breen  mine  sandstone  is  found  in  some  places  underlying  the  ferruginous 
schists.  This  phenomenon  is  accounted  for  in  the  supposition  that  the 
schists  formed  an  overhanging  cliff  in  the  Potsdam  sea,  in  which  the 
sands  accumulated.  From  the  structure  of  some  of  the  ore  in  the  mine  the 
author  is  inclined  to  regard  it  as  having  been  formed  by  the  dissolving  of 
silica  from  ferruginous  jaspers. 

1880. 

Beooks,  T.  B.  The  geology  of  the  Menominee  iron  region  (east  of  the  center 
of  R.  17  E.),  Oconto  County,  Wisconsin:  Geology  of  Wisconsin,  Survey  of  1873-1879, 
vol.3,  pp.  129-599.     With  maps  and  plates.     Atlas  Plates  XXVIII,  XXIX.     1880. 

Although  primarily  an  account  of  the  geology  of  the  Menominee 
district  on  the  west  side  of  the  Menominee  River,  this  report  includes  also 
a  description  of  the  geology  of  that  portion  of  this  district  which  lies  in 
Michigan. 

The  Menominee  district  in  Michigan  is  divided,  as  in  the  author's  earlier 
reports,  into  a  north  and  a  south  belt,  of  which  only  the  latter  concerns  us. 
The  south  belt  in  turn  is  divided  into  a  north  and  a  south  range,  in  the 
latter  of  which  the  principal  mines  are  opened. 

The  rocks  of  the  Menominee  district  are  grouped  as  follows,  beginning 
with  the  youngest: 

„  .  ,  ,         -i    /J  -j-ix  f  Sand  and  gravel  (Champlain?). 

Superficial  deposits  (dritt) ■{  ^      ,,       V"      ,^..\.      ,     .  , 

'■  IV  I  Bowlder  clay  (tdl),  glacial. 

„.,     .  f  Calciferous  sand  rock  and  limestone. 

Lower  Silurian {  ^,^    ,t       ,  j^         /r>  i.  j      \ 

I  St.  Mary  8  sandstone  (Potsdam) . 

Keweenaw  ( copper  series ) Wanting. 

Granite  (eruptive?),  gneiss,  liornblende, 


Huronian  (iron  bearing). 


Tipper.. 


actinolite,  mica-,  chlorite-,  and  quartz- 
scliists,  iron  ores,  clay  and  carbonaceous 
slate,  quartzite,  and  conglomerate. 
Middle  . .  .Clay  slate  and  quartzite. 

-  Lower Dolomite,  iron  ore,  and  quartzite. 

Laurentian  (not  subdivided) Granite,  gneiss,  and  crystalline  schists. 


64  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

In  a  second  table  (facing  p.  437)  the  Huroniau  rocks  are  divided  into 
two  groups — an  eruptive  group,  embracing  diorite,  gabbro,  granite,  and 
diabase,  and  a  metamorphic  group,  including  granite,  greenstone,  syenite, 
quartzite,  limestone,  and  the  various  schists  so  abundant  in  the  district. 
In  the  Menominee  region  the  granite  is  declared  to  exist  as  dikes,  which 
are  said  to  be  more  frequent  in  the  upper  division  of  the  series  than  in  the 
lower  divisions.  The  diorites  and  gabbros  occur  as  conformable  beds. 
Most  of  them  are  believed  to  be  metamorphosed  sediments.  The  Lauren- 
tian  rocks  are  likewise  separated  into  an  eruptive  group,  which  includes 
granite  and  greenstone,  and  a  group  composed  of  metamorphosed  sediments. 
This  latter  group  includes  gray  granites,  gneisses,  and  schists,  with  the 
addition,  probably,  of  granulite  and  quartzite. 

In  the  first  chapter  of  the  report  the  author  describes  the  Huronian  and 
Laurentian  series  in  some  detail.  The  Lower  Huronian  includes  beds 
I-VII.  Of  these,  beds  I,  III,  and  IV  are  little  known.  Bed  II  is  the  great 
lower  quartzite  and  bed  V  the  great  marble  bed,  which  in  the  Sturgeon 
River  district  is  almost  as  prominent  as  the  quartzite.  Overlying  the  mar- 
ble is  the  great  iron  horizon.  It  is  coextensive  with  the  marble.  This  belt 
is  best  exposed  along  the  line  of  the  Chicago  and  Northwestern  Railway. 
It  is  believed  to  be  connected  with  a  similar  ore  belt  north  of  Lake  Antoine 
by  an  anticline  which  pitches  westward  under  Wisconsin. 

The  Middle  Huronian  members  include  beds  VIII-XIII.  They  consist 
of  quartzites,  clay  slates,  and  schists. 

The  Upper  Huronian  embraces  mica-schists,  gneisses,  and  granites.  It 
comprises  beds  XIV-XX,  represented  best  in  the  exposures  on  and  near 
the  Menominee  River.  The  schists  of  the  series  dip  at  a  high  angle  to  the 
south,  and  apparently  underlie  the  granite  and  gneiss  observed  south  of  the 
Big  Quinnesec  Falls. 

In  consequence  of  the  sharply  folded  character  of  the  Menominee 
rocks,  the  total  thickness  of  the  series  can  not  be  estimated  with  a  close 
degree  of  accuracy.  Excluding  the  granite  (bed  XX),  which  the  author  is 
inclined  to  regard  as  eruptive,  the  thickness  of  the  series  is  supposed  to  be 
from  10,000  to  15,000  feet.  This  estimate  is  from  4,000  to  9,000  feet  less 
than  that  obtained  by  the  measurement  of  the  individual  beds  at  different 
places  within  the  limits  of  the  district  and  the  addition  of  the  results  thus 
obtained. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  65 

Approximate  thickness  of  the  Hwronian  strata  in  the  Menominee  region. 


Bed. 

Where  observed. 

Maximum 
thickness. 

XIX 

Michigamme  River                    .           ..         

Fed. 
4,000 

XVIII 

Brule  River                        

1,900 

XVII 

Pine  River .   

1,400 

XVI 

Sturgeon  Falls 

1,700 

XV 

Sturgeon  Falls 

900 

XIV 

Pine  River 

800 

XIII 

Fourfoot  Falls 

700 

XII 

Fonrfoot  Falls 

200 

XI 

Fourfoot  Falls 

1,000 

X 

.300  (?) 
400  (?) 
1,000  (?) 
700 

IX 

VIII- VII  .. 

Lake  Hanburv 

VI 

South  belt  iron  formation 

V 

Marble,  south  belt 

1,700 

IV-IIJ 

Pine  Creek 

1,000  (?) 
1,000  (?) 
300 

II 

Sees.  7,  8,  T.  39  N.,  R.  28  AV. 
Falls  of  Sturgeon  River 

,  Michigan 

I 

19, 000 

The  character  of  the  different  formations  met  with  in  the  Menominee 
district  and  their  equivalency  with  the  beds  constituting  tlie  Marquette 
Huronian  are  exhibited  in  the  following  table.  The  correlation  of  the 
Menominee  rocks  with  those  of  the  Marquette,  the  Penokee,  and  the  Sunday 
Lake  series  is  so  complete  that  the  author  thinks  that  it  points  to  the  fact 
that  the  rocks  of  these  different  districts  were  all  formed  in  one  basin  under 
essentially  like  conditions. 

The  Roman  numerals  affixed  indicate  to  which  beds  of  the  Marquette 
series,  as  worked  out  by  the  author,  the  Menominee  beds  correspond. 

Table  showing  the  character  of  the  formations  in  the  Menominee  district  and  their 
equivalency  with  those  of  the  Marquette  district. 

XX.  Granite,  rarely  gneissic,  perhaps  also  including  the  rocks  at  Peminee  Falls. 
XIX.  Hornblende-  and  tremolite-schist,  greenstone,  gabbro,  and  diabase.     The  gabbro  has  the 

appearance  of  being  eruptive. 
XVII.  Gneisses  and  schists. 
XVI.  Gabbro,  diorite,  diabase,  and  schistose  greenstones. 

Sericite-  ,  magnesian,  and  greenstone-schists,  and  serpentine. 

MON   XLVI — 04 5 


66  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

XV-VIII.  Covered  by  drift  in  Menominee  Vallej',  in  vicinity  of  Quinnesec.     At  moutti  of  Sturgeon 
Eiver  covered  with  drift  for  a  mile  soutli  of  bed  XYI.     Lower  portion  of  series  consist  of 
slates,  greenstones,  slates,  quartzite  and  mica-schist,  and  greenstone. 
VII.  Hydromicaceous  schist,  graduating  into  clay  slate. 
YI.  Iron  ore. 
Y.  Dolomitic  marble. 
lY-III.  Covered. 
II.  Quartzite. 
I.  Chloritic  gneiss,  hydrous  magnesian  schists,  slate  conglomerates,  quartzite,  and  perhaps 
diorite  (may  belong  with  Laurentian). 
Nonconformable  with  Laurentian. 

Many  details  are  given  concerning  the  exposures  of  each  of  the 
formations,  and  a  number  of  large-scale  maps  are  published  which  exhibit 
well  the  distribution  of  these  exposures  in  different  portions  of  the  district. 

The  iron-ore  rocks  include  magnetites,  magnetic  quartzose,  and  mag- 
netic amphibole  rocks;  specular  hematites  and  martites;  siliceous,  jaspery, 
and  argillaceous  hematites;  and  limonitic  quartzose  ore.  Tlu'ee  beds  have 
produced  merchantable  ore,  viz,  VI,  XV,  XIII.  The  magnetites  and  the 
specular  hematites  grade  into  each  other  through  martite  and  the  hematites 
into  limonites,  but  the  latter  do  not  pass  into  magnetites. 

The  quartzites  are  sometimes   conglomeratic  and  sometimes  schistose. 

The  occurrence  of  conglomerates  at  the  Falls  of  the  Sturgeon  is 
described  in  great  detail.  The  author  is  now  assured  that  they  mark  an 
unconformity  between  the  Laurentian  granites  and  g-neisses  and  the  Huronian 
beds. 

The  sequence  of  rocks  beginning  at  the  basin  below  the  falls,  i.  e,, 
between  the  quartzites  and  the  granite-gneiss  complex,  is  given  as  follows: 

1.  On  the  south  side  of  this  point,  hence  forming  the  north  shore  of  the  basin, 
is  a  considerable  bed  of  a  soft,  fine-gnxined  rock,  apparently  a  chloro-argillaceous, 
arenaceous  schist.  *  *  *  The  strong  cleavage  planes  strike  N.  80-  W.,  dip 
60°  S.  A  somewhat  distinct  banding  had  a  strike  N.  75°  W.,  and  vertical  dip.  As 
no  rock  is  exposed  for  some  distance  south,  this  schist  may  have  considerable 
thickness,  and  in  j^art  underlie  the  basin. 

2.  North  of  the  schist  is  S  feet  in  thickness  of  a  reddish-gray  quartzite. 

3.  A  thin  bed  of  a  schistose  conglomerate  holding  pebbles  of  what  appear  to 
be  Laurentian  granite  and  gneiss  and  white  quartz,  loosely  bedded  in  a  matrix 
resembling  1.     *     *     * 

4.  Five  feet  of  schist  similar  to  1. 

5.  Eight  feet  of  conglomerate  similar  to  3. 

6.  Three  feet  of  schist  similar  to  1,  which  brings  us  to  a  narrow  part  of  the  river 
and  ends  the  series,  for  on  the  opposite  side  is  Laurentian  granitic  gneiss.     *    *     * 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  67 

The  bedding-  of  the  coiig-lomerate  and  schistose  beds  1  to  6,  above  described, 
was  unmistakable,  being-  N.  80°  W.,  with  vei'tical  dip;  hence  essentially  parallel 
with  the  great  Huronian  quartzite  which  overlies  them  on  the  south.     *     *     ->^ 

The  structural  facts  in  connection  with  the  strong-  lithological  affinities  which 
the  schist-conglomerate  series  bear  to  the  Huronian,  and  the  still  more  important 
fact  that  the  pebbles  contained  in  the  conglomerate  are  unmistakablj^  Laurentian, 
leave  no  question  in  my  own  mind  but  that  the  rocks  under  consideration  are 
Huronian,  and  form  the  base  of  the  series  at  this  point  [pp.  467-468]. 

Tlie  dolomitic  marble  is  qnartzitic.  It  is  associated  with  beds  of 
uovacnlite  and  clay  slates.  The  latter  rocks  are  found  also  as  beds  inter- 
stratified  with  quartzites  and  actinolite-schists,  as  layers  alternatino-  with 
the  ores  and  with  mag-nesian  schists,  and  as  independent  beds  constituting  a 
distinct  fornnation. 

The  chloritic  rocks  are  so  closely  related  to  the  argillaceous  ones  that 
the  author  finds  it  difficult  to  draw  the  line  between  the  two.  On  the  one 
hand  the  schists  appear  to  grade  through  argillo-chloritic  schists  into  clay 
slates  and  iron  ores,  through  quartzose  varieties  into  quartzites  and  through 
micaceous  varieties  into  inica-schists ;  and  on  the  other  hand  they  appear 
to  grade  into  diabases  and  diorites,  of  which  they  seem  to  be  altered 
varieties. 

The  greenstones  include  diabases  and  diorites  and  a  series  of  fine- 
grained undetermined  rocks  that  appear  to  be  connected  with  these.  The 
special  forms  of  greenstone  that  have  been  made  out  are  diorite,  diabase, 
gabbro,  and  serpentine.  These  grade  into  hornblende  rock,  hornblende- 
gneiss,  mica-schist,  mica-gneiss,  chlorite-schists,  and  kersantite. 

The  schists  occurring-  along  the  Menominee  River  are  actinolite-schists, 
tremolite-schists,  micaceous  schists,  and  sericite-schists.  The  rocks  formerly 
supposed  to  be  talcose  schists  are  now  known  to  be  sericite-schists. 

Of  the  maps  accompanying  the  volume  in  which  Brooks's  report  is 
published  two  are  by  the  author,  with  the  assistance  of  C  E.  Wright 
and  others.  The  most  important  of  these  is  the  geological  "map  of  the 
Menominee  iron  region,"  a  portion  of  which  is  reproduced  in  PI.  IV. 
This  map  illustrates  the  distribution  of  exposures  within  the  district  studied. 
It  is  accompanied  by  two  sections,  one  along  the  line  C-C  passing-  between 
Lakes  Antoine  and  Fumee,  and  the  other  along  the  line  D-D  near  the 
Sturgeon  River.     These  are  reproduced  in  figs.  8  and  9. 

The  second  map  embodies  the  author's  views  concerning  the  folding  of 


68 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


the  district. 


^_        0)  ^    =s 


\ 


I   c  S 


On  it  are  two  ideal  sections  illustrating  his  conception  of  the 
folding  in  the  neighborhood  of  Quinuesec  and  in  the  vicinity 
of  Iron  Mountain.     (See  figs.  10  and  11.) 

"WiCHMANN,  Aethuk.  Micr'oscoplcal  ob- 
servations of  the  iron-bearing  (Huronian) 
rocks  from  the  region  south  of  Lake  Superior. 
Geology  of  Wisconsin,  Survey  of  ]  8T3-1879, 
vol.  3,  pp.  600-656.     1880. 

Many  of  the  rocks  of  the  Marquette 
and  the  Menominee  districts  were  submit- 
ted to  Dr.  Wichmann  for  microscopical 
study.  His  results  are  embodied  in  the 
paper  which  constitutes  Chapter  V  of 
Brooks's  report.  Among  the  rocks  de- 
scribed from  the  Menominee  district  may 
be  mentioned  siliceous  dolomite,  quartz- 
ite,  actinolite- magnetite -schist,  serpen- 
tine, diabase,  quartz-diabase,  mica-gneiss, 
sericite-gneiss,  chlorite-mica-schist,  cal- 
careous mica- schist,  sericite- schist, 
hornblende-schist,  clay  slates,  and  cal- 
careous and  feiTuginous  sandstones. 
The  serpentine  is  said  to  occur  in  sec. 
27,  T.  39  N.,  R.  29  W. 


B  £ 
2  o 


i  «.2 


O   ' 


5  S  ^ 


>  -^    ■- 

i'g| 


he  fao 


PS   o  ■«   o 


Brooks,  T.  B.  Sketch  of  the  Laurentian 
rocks  of  Michigan.  Geolog}^  of  Wisconsin, 
Survey  of  1873-1879,  vol.  3,  pp.  661-663. 
1880. 


g»'f:i  Mica-gneiss,    hornblende -gneiss, 

I  III  hornblende-schist,  chloritic  gneiss,  gran- 
M  ll  ite,  and  hornbleudic  gi-anite  are  declared 
bv  Brooks  to  be  the  characteristic  rocks 
of  the  Laurentian  in  Michigan.  Horn- 
blende-schists are  said  to  be  especially 
abundant  in  the  Menominee  district.  By 
the  alteration  of  the  hornblende  into  chlorite,  the  horn- 
blende-gneiss passes   into   chloritic   gneiss,  which   also  is 


I  ■■§  s  I 


abundant  in  the  Menominee  district. 


The  srranite  is  "that  extreme  massive 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE. 


69 


variety  of  gneiss  in  whicli  all  interior  evidence  of  bedding  is  obliterated 
by  metamorphic  action.  I  assume  it  to  be  an  altered  sedimentary  rock, 
as  it  apparently  must  be  from  its  structural  relations  with  the  other  beds, 
the  granite  dikes  and  certain  great  irregular  red  masses  not  being  included" 
(p.  662).  Among  the  varieties  of  granite  observed  in  the  Menominee  dis- 
trict, a  red,  massive  granite,  a  fine-grained,  white  variety,  and  a  porphyritic. 


Upper 

-Sv^ 

Lower                              V* 

Lower 

/ 

Granite      / 
1 
1 

1 

1 

/       / 
/        / 
/       / 
/       / 

/       / 

// 

/ \„ 

1"     Granite 
0  (Laurentian) 

3  milea  (approx.) 


Fig.  10. — structure  section  across  the  Menominee  region  tlirough  tlie  west  end  of  Lake  Fiimee.    After  T.  B.  Brooks.  1880. 

gneissoid  variety  are  most  common.     The  hornblendic  granite  is  not  found 
in  the  Menominee  district. 

The  superposition  of  the  beds  in  the  Laurentian  can  not  often  be  made 
out,  owing  to  the  complicated  folding  and  the  uniformity  in  the  lithological 


Upp 

-^/Middle--.                /                 ..-Ubwer-. 

'<."'     Upper 

/ 
/ 
/ 

I'  / 

( 

1       / 

/ 
/ 

/ 

V    \ 

w 

\ 

\ 

/ 

XiH.  XVIII 

XV 

XIV 

IX         VI                                                    II                          0 

V                                                               ' 

I 

2  miles 

(approximate) 

Fig.  11.— Structure  section  across  the  Menominee  district  in  the  vicinity  of  Twin  Falls.    After  T.  B.  Brook.?,  1880. 

character  of  the  different  rocks.     Cutting  these  rocks  are  granite  and  g-reen- 
stone,  among  the  latter  of  which  are  Some  dolerites. 

Wright,  Charles  E.  The  geology  of  the  Menominee  iron  region  (economic 
resources,  Hthology  and  westerlj^  extension).  Geology  of  Wisconsin,  Surve}'  of 
1S73-1S79,  vol.  3,  pp.  665-734,  and  atlas  sheet  xxx.     1880. 

In  Brooks's  report  the  chief  interest  centers  in  the  scientific  problems 
presented  by  the  Menominee  iron  region.  In  the  present  report  Wright 
deals  with  the  economic  geology  of  the  district.  He  describes  the  progress 
of  the  work  at  each  of  the  mines  in  operation  in  1879,  gives  analyses  of 
their  ores,  and  mentions  some  interesting  details  concerning  the  relation  of 
the  ore  bodies  to  the  surrounding  rocks  in  some  of  the  mines.  At  the 
Vulcan  mine  an  ore  lens  occurs  in  the  midst  of  jaspery  schists,  into  which 


70  THE   :\JEXOMINEE  IRON-BEARING  DISTRICT. 

the  former  passes  without  any  break  in  the  stratification.  The  author's 
impression  regarding  the  Menominee  ore  deposits  is  that  they  are  of  a 
secondary  nature.  He  thinks  that  the  ores  "were  originally  the  same  as 
the  jaspery  specular  schists  in  which  they  occur,  and  have  been  brought  to 
their  present  condition  by  the  dissolving  out  of  the  silica  from  the  lean 
schists"  (p.  671). 

The  author  is  inclined  to  the  opinion  that  at  the  Saginaw  mine,  in  the 
southwest  quarter  of  sec.  4,  T.  39  N.,  R.  29  W.,  there  is  a  narrow  syncline  in 
the  marble  beds.  If  this  is  a  fact,  it  points  to  the  existence  of  a  second  ore 
belt  to  the  south  of  the  one  on  which  the  mine  is  situated,  and  it  is  on  the 
eastward  extension  of  this  second  belt  that  the  Vulcan  and  Curry  mines  are 
opened.  On  the  east  side  of  the  Norway  property  the  formation  is  much 
disturbed  and  some  of  the  beds  are  actually  brecciated.  At  the  Quinuesec 
mine  the  formation  has  a  dip  of  70°  N.  South  of  the  ore  belt  the  dip 
becomes  steeper,  then  vertical,  and  then  there  is  a  southerly  dip.  From  a 
consideration  of  other  phenomena  the  author  thinks  there  is  here  an  indica- 
tion of  an  anticline  dipping  west,  and  that  this  again  indicates  a  second 
ore  belt  farther  south. 

Nearly  all  the  ores  are  declared  to  be  strictly  first  class.  "Many  of 
them  contain  quite  a  percentage  of  lime,  magnesia,  and  alumina,  all  desir- 
able elements  as  impurities.  *  *  *  The  sulphur  in  the  majority  of 
these  ores  is  hardly  worth  considering,  while  the  phosphorous  is  remarkably 
low"  (p.  678). 

In  Chapter  II  the  author  describes  the  lithology  of  the  beds  constitut- 
ing the  Huronian  series.  He  divides  the  rocks,  on  the  basis  of  a  microscop- 
ical examination,  into  calcareous  rocks,  quartzose  rocks,  including  quartzites, 
mica-schists  and  various  quartz-schistS,  liornblende-schists,  and  hornblende 
rocks;  greenstones,  including  diorite  and  diabase;  and  schists  and  slates, 
including  chloritic,  talcose,  and  argillaceous  varieties.  The  chloritic  schists 
are  closely  allied  to  the  greenstones.  Their  manner  of  association  indicates 
that  they  ma}-  be  greenstone  tuff's,  although  it  is  possible  that  they  may  be 
metamorphic  beds.  The  microscopical  features  of  all  the  different  varieties 
of  all  these  rocks  are  briefly  described.  Among  the  greenstones  one  diabase 
is  recognized,  though  it  does  not  occur  on  the  Michigan  side  of  the  river. 

The  map  accompanying  the  report  exhibits  only  the  distribution  of  the 
iron  formation  and  the  greenstones.  It  contains  no  information  not  on 
Brooks's  map. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  71 

Numerical  index  to  specimens  from  the  Menominee  region.  Described  by 
Messrs.  Broolcs,  Wicliman,  Wright,  and  others.  Geology  of  Wisconsin,  Survey  of 
1873-1879,  vol.  3,  pp.  735-741.     1880. 

This  is  a  list  of  the  specimens  collected  by  the  above-named  authors 
from  various  portions  of  the  Menominee  district. 

1881. 

RoMiNGER,  C.  Menominee  iron  region:  Geol.  Surv.  Michigan,  vol.  i,  pp. 
157-2il.     1881. 

In  his  report  on  the  geology  of  the  Menominee  district  Rominger  does 
not  attempt  to  classify  the  rock  beds  into  groups,  as  they  were  arranged  in 
the  report  on  the  Marquette  district,  but  describes  in  minute  detail  a  large 
number  of  exposures  in  the  district  and  makes  a  few  general  remarks  on 
the  succession  of  the  beds,  comparing  them  with  the  succession  in  the 
Marquette  district.  At  the  Bi'een  and  the  Emmett  mines,  the  most 
easterly  ones  on  the  range,  the  ore-bearing  beds  are  seen  to  dip 
south,  the  highest  beds  being  white  and  red  mottled  hydrornica- 
schists.  Below  these  is  a  large  series  of  thin-bedded  siliceous  and 
argillaceous  rocks  impreg-nated  with  hematite  and  martite.  Interlami- 
nated  between  them  are  seams  of  nonstratified,  reddish-brown  ore,  which 
"are  evidently  a  secondary  product  of  lixiviation  of  the  strata  b}'  per- 
colating water"  (p.  158).  In  the  pits  of  the  Breen  mine  there  is  a  contact 
of  the  Silurian  sandstone  with  the  neai-ly  vertical  strata.  The  lower 
ledges  of  the  sand  rock  generally  consist  of  a  breccia  containing  angular 
fragments  of  ore  and  of  the  ore-bearing  rocks.  Cracks  and  cavities  in  the 
Huronian  rocks  are  often  filled  with  sandstone,  so  that  in  some  places  the 
younger  sandstone  appears  to  be  beneath  the  older  schisfs.  After  tracing 
the  ore  belt  to  the  west,  lie  concludes  that  the  ore- bearing  series  amounts 
to  more  than  1,000  feet  in  thickness.  North  of  it  are  ridges  of  limestone, 
and  north  of  the  limestone  is  a  large  series  of  "flaggy  rock  beds,  richly 
impregnated  with  bright  specvilar  iron-oxide  granules."  The  rocks  are 
sandy  quartzose  beds  that  are  often  so  richly  bespangled  with  hematite  as 
to  resemble  the  specular  ore  of  the  Marquette  range.  North  of  this  ore 
belt  no  rocks  are  met  with  for  a  quarter  of  a  mile,  when  a  belt  of  quartzite 
ledges  is  reached  having  a  thickness  of  not  less  than  1,000  feet.  The 
quartzite  dips  noi'therly,  sometimes  northwest,  and  sometimes  northeast, 
and  rests  unconformably  on  the  granite  at  the  Falls  of  the  Sturgeon  River. 


72  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

South  of  the  East  Vulcan  mine,  on  the  west  hne  of  sec.  13,  T.  39 
N.,  R.  29  W.,  crystalline  diorites  are  apparently  interbedded  with  slates  and 
quartzites.     They  are  regarded  as  intrusive. 

The  rocks  west  of  the  East  Vulcan  are  the  same  in  character  as  those 
east  of  the  mine,  and  their  relations  to  one  another  are  the  same.  lu  the 
western  of  the  Vulcan  pits  the  ore  beds  dip  only  20°  to  30°,  though  in  the 
eastern  pits  they  are  nearly  vertical.  The  hills  south  of  Lake  Hanbury  are 
formed  of  "a  large  succession  of  dark,  blackish-colored  clay  slates,  merging 
into  various  modifications  of  lighter  gray-colored,  pale  silky -shining 
micaceo-quartzose  and  feldspathic  schists,  which  contain  a  considerable 
proportion  of  carbonate  of  lime,  or  of  sparry  carbonate  of  iron,  and  of 
numerous  interlaminated  belts  of  dark-colored  granular  quartzites"  (p.  164). 

The  author  agrees  with  Major  Bi'ooks  in  supposing  a  repetition  of 
strata  in  this  belt  of  exposures,  one-fourth  of  a  mile  wide,  due  to  plication, 
although  he  could  observe  "no  synclinal  and  anticlinal  position  of  the 
ledges."  On  the  north  side  of  the  ledges  the  dip  is  clearly  southward,  in 
the  center  of  the  ledge  it  is  vertical,  and  on  the  south  side  in  many  places 
a  northern  dip  is  observed,  but  no  significance  is  attach(;d  to  the  phenomena. 

North  of  the  Curry  mine  it  is  noticed  that  the  upper  layers  of  the 
liiTiestone  formation  are  quartzitic  and  sometimes  brecciated.  Occasionally 
beds  of  conglomerate  are  interbedded  with  the  series,  whose  thickness 
here  amounts  to  about  400  to  500  feet.  In  the  pits  of  the  Saginaw  mine  in 
the  southwest  quarter  of  sec.  4,  T.  39  N.,  R.  29  W.,  the  ore  belt  is  inclosed 
in  well-laminated,  thin-bedded,  partly  siliceous,  partly  argillitic  beds  rich  in 
iron  oxides.  At  the  Norway  mine  the  limestone  appears  to  be  underlain 
by  light-colored,  reddish,  gray,  or  greenish  slates,  interbedded  with  which 
are  arenaceous  seams  rich  in  mica  scales. 

At  the  Cyclops  mine  is  another  xinconformable  contact  of  the  Silurian 
sandstone  upon  the  Huronian  schists.  Here  the  latter  rocks  are  hollowed 
out  into  a  trough  in  which  the  sandstone  is  deposited. 

The  creek  draining  Lake  Fumee  passes  through  the  limestone  forma- 
tion in  sec.  35,  T.  40  N.,  R.  30  W.,  exposing  several  successive  synclinal 
and  anticlinal  arches,  the  measured  thickness  of  the  beds  being  600  to  700 
feet.  The  limestone  here  is  dolomitic.  It  contains  larg-e  belts  of  calcare- 
ous breccia,  and  is  often  full  of  quartzose  seams  parallel  to  the  stratification. 
Certain  ledges  consist  exclusively  of  flinty  quartz. 

The  author  also  notes  the  existence  of  a  range  of  limestone  hills  north 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  73 

of  Lake  Fumee  and  an  outcropping'  of  quartzite  south  of  it.  The  quartzite 
is  considered  to  be  identical  with  the  upper  quartzose  beds  of  the  limestone 
formation,  and  not  to  be  equivalent  to  the  lower  quartzite  at  the  Falls  of 
the  Sturgeon  River. 

This  limestone  ridge,  surrounded  on  lioth  sides  by  low,  swampy  lands,  is  directly 
north  of  the  limestone  belt  which  underlies  the  ore  formation  at  the  Norway  and 
Stephenson  mines,  a  little  over  a  mile.apart  from  it,  with  a  swamp  valley  between  them. 
Both  belts  dip  to  the  south.  We  must  therefore  either  suggest  a  rupture  of  the 
rock  belt  in  the  intervening  space,  or  an  intervening  synclinal  trough  connecting 
the  two.  The  same  correspondence  in  dip  exists  between  the  limestone  bluffs  on 
the  roadside  near  Quinnesec  and  the  equivalent  quartzose  belts  on  the  north  side  of 
Lake  Fumee;  but  in  that  case  we  can  prove  by  natural  exposures  the  occurrence  of  a 
repeated  plication  of  the  rock  belt  in  the  intervening  space.  Besides  the  locality 
already  mentioned  in  which  this  plication  of  the  beds  is  seen,  there  is  another  one 
handy  for  observation  in  the  southeast  quarter  of  the  northeast  quarter  of  sec.  34, 
on  the  roadside  to  Lake  Antoine,  where  the  limestones  dip  northward  in  anticlinal 
position  with  the  more  southern  outcrops.  An  anticlinal  position  exists  also  between 
the  limestones  exposed  in  the  south  slope  of  the  Quinnesec  ore  range  and  those  on 
the  north  slope  of  the  range  dipping  under  the  bed  of  Lake  Antoine,  and  great 
probability  exists  for  the  occurence  of  a  synclinal  trough  of  limestone  in  the  place 
where  the  basins  of  Lake  Antoine  and  Lake  Fumee  are  now  [p.  181]. 

Recapitulating  the  so  far  ascertained  facts,  we  have  become  acquainted  with 
three  distinct  groups  of  rock,  one  succeeding  the  other  conformably,  or  at  least  in 
direct  superposition  on  the  other.  The  most  southern,  seemingly  uppermost,  is  a 
series  of  dark,  gray-colored  slaty  or  schistose  beds,  with  interlaminated  quartzose 
belts,  amounting  to  a  thickness  of  perhaps  over  2,000  feet,  which  I  will  call  the  Lake 
Hanhury  slate  group.  A  second  group  next  succeeding  it  consists  in  the  upper 
part  of  light-red,  or  whitish,  or  gray-colored,  hydromicaceous  and  argillitic  strata: 
in  the  lower,  of  siliceous  beds  richly  impregnated  with  iron  oxide  in  the  amorphous 
hematitic  condition,  or  in  the  crystalline  form  of  raartite,  with  metallic  luster,  which 
lower  series  incloses  seams  almost  exclusively  composed  of  martite  granules,  consti- 
tuting the  economically  valuable  ore  deposits.  This  group  I  will  name  the  Quinnesec 
ore  formation;  it  amounts  to  a  thickness  of  not  less  than  1,000  feet,  but  locally, 
perhaps,  it  is  much  thicker.  The  third  group  is  formed  of  a  series  of  light-colored 
quartzite  and  limestone  beds  of  a  siliceous  character,  usually  in  part  of  a  brecciated 
structure,  and  also  amounting  to  at  least  1,000  feet  in  thickness,  which  I  will  call  the 
Norway  limestone  helt.  All  these  strata  are  upheaved  in  a  certain  axial  direction, 
which  is  about  west-northwest,  and  dip  southward,  if  we  consider  them  as  a  body, 
and  overlook  folds  of  the  strata  and  other  local  irregularities  [p.  182]. 

The  author  is  not  certain  that   the  succession  here  given  and  the 
succession  as  marked  out  to  the  north  and  to  the  south  of  this  known  belt 


74  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

is  correct,  because  of  the  difficulty  of  deciding  properly  as  to  the  relative 
positions  of  the  rock  beds,  on  account  of  folding,  faults,  and  the  covering 
of  critical  areas  by  drift. 

North  of  the  limestone,  in  the  southwest  quarter  of  sec.  7,  T.  39  N., 
R.  28  "W.,  the  author  tinds  an  occurrence  of  siliceous  specular  flag  ores 
dipping  southward  under  the  limestone,  which  also  has  a  southern  dip. 
Again,  north  of  the  Norway  mine  is  a  belt  of  micaceous  slaty  argillites  over 
200  steps  in  width,  and  in  the  southeast  quarter  of  the  southeast  quarter  sec. 
32,  T.  40  N.,  R.  29  W.,  is  a  series  of  siliceous  flags,  argillites,  and  quartzose 
beds,  consisting  of  alternating  narrow  bands  of  a  jaspery  quartz  and  of  a 
compact  siliceous  iron  ore.  North  of  this  bed  again  is  a  bed  of  graphitic 
slate  8  feet  wide,  beds  of  banded  micaceous  quartz-schists,  and  again 
graphitic  slates.  This  recurrence  of  beds  to  the  north  of  the  principal 
iron-bearing  formation  is  explained  as  due  to  a  synclinal  trough,  supposed 
to  exist  in  the  limestone.  This  supposition  requires  the  turning  over  of  the 
series  as  usually  seen.     To  quote  the  author: 

The  hitherto  described  rock  series  of  the  Menominee  iron  range  allows  a  much 
more  simjale  and  harmonious  explanation  of  its  structure  if  we  suggest  a  synclinal 
trough  of  limestone  in  this  place  and  revert  the  generally  observed  order  in  the 
superposition  of  the  rock  beds,  considering  the  most  southern,  apparently  highest 
rock  beds  of  the  Lake  Hanbury  series  as  the  lowest,  directly  succeeding  above  the 
diorites  south  of  the  Menominee;  next  higher  would  be  the  iron  formation,  and 
highest  or  youngest  the  limestone  formation  and  strata  north  of  it.  This  order 
is  actually  exhibited  on  the  east  side  of  Sturgeon  River  *  *  *  and  in  the 
Chapin  mine  and  Quinnesec  mine.  In  all  other  described  localities,  according  to  this 
theory,  which  I  believe  to  be  the  fact,  the  strata  have  been  placed  in  an  overtilted 
position  by  the  upheaval  acting  most  powerfully  from  south  to  north,  whereby  the 
limestones  came  to  lie  beneath  the  others,  and  were  by  me  at  first  mistaken  for  the 
oldest  in  the  succession  [p.  186]. 

Immediately  north  of  Pine  Creek,  in  T.  40  N.,  R.  29  W.,  are  ridges  of 
quar.zite,  and  north  of  them,  and  apparently  in  discordant  contact  with  the 
quartzites,  are  bluffs  of  granite.  This  great  quartzite,  over  1,000  feet  thick, 
begins  in  sec.  10,  T.  39  N.,  R.  28  W.,  and  runs  westward  in  an  almost  contin- 
uous ridge  to  the  Falls  of  the  Sturgeon  River  and  beyond  for  the  distance  of 
a  mile  or  so.  Of  the  limestone  belt  shown  in  Major  Brooks's  map  south 
of  the  falls  Dr.  Rominger  did  not  see  the  slightest  evidence. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  75 

The  relations  between  the  quartzite  and  granite  at  the  falls  are  thus 
described : 

The  bed  rock  of  the  falls  is  granite,  which  evidently  forms  here  an  arched, 
bubble-like  protrusion,  dipping  in  all  directions;  the  sedimentarj^  strata  above  this 
bubble  have  likewise  been  pushed  aside  with  the  same  irregularity.  Thej'  have  in 
places  become  entangled  between  the  granite,  and  seem  to  dip  under  it,  but  the  same 
ledges  are  seen  in  another  place  dipping  in  a  different  direction  and  to  lie  above  the 
granite.  *  *  *  Interstratified  with  the  granite  are  belts  of  dark  diorite-like 
rock,  consisiting  of  quartz,  white,  probably  anorthic  feldspar,  and  of  a  large  pro- 
portion of  black  mica.  *  *  *  In  intimate,  seemingl}'  conformable  contact  with 
the  granite  occurs  a  series  of  schistose  beds,  which  are  exposed  at  the  foot  of  the  falls 
in  an  almost  vertical  position,  but  they  seem  to  be  in  an  anticlinal  position  on  the 
two  sides  of  the  river.  On  the  west  side  are  stratified  red-colored  feldspathic  rocks, 
crowded  with  granules  of  magnetite  and  witli  iron  pyrites  in  small  cubes;  with  them 
occur  narrow  seams  of  a  rich  granular  magnetic  ore  contaminated  with  iron  pyrites. 
This  belt  amounts  to  about  8  or  10  feet,  and  the  strata  dip  under  the  granite.  Next 
and  below  it  is  a  rock  belt,  10  feet  wide,  of  schistose,  feldspathic,  and  sericitic  beds; 
then  comes  a  seam  of  compact,  finely  granular,  red  feldspar  20  feet  wide.  *  *  * 
Under  it  succeed  silky,  shining  gray  sericite-schists,  with  a  feldspathic  groundmass; 
then  a  break  in  the  formation  occurs,  and  the  same  feldspathic  sericite-schists  dip  in 
an  opposite  direction,  away  from  the  granite,  and  farther  on  in  this  direction  we  soon 
come  to  quartzite  ledges,  apparently  incumbent  on  them.  On  the  east  side  of  the 
river  we  find  similar  hard  sericite-schists,  with  interlaminated  granular  feldspar 
seams,  and  with  several  belts  [of]  a  coarse  conglomerate  rock  formed  of  red  granite 
pebbles  and  of  white  quartz  pebbles,  some  of  them  opalescent.  The  cement  is  the 
schistose  sericite.  Some  of  the  granular  feldspathic  beds  of  the  schists  are  distinctly 
ripple  marked.  Going  across  this  schistose  belt,  which  amounts  to  about  100  feet, 
we  come  again  into  granite,  which  seems  to  be  in  conformable  contiguity  with  the 
schists.  We  have  here  evidentlj^  a  series  of  sedimentary  beds  deposited  on  a 
granitic  substratum,  which  during  the  upheaval  became  wedged  in  between  the 
plastic  granite  mass,  tilting  and  overlapping  them  locally,  so  as  to  appear  as  the 
lower  beds  [pp.  190-192]. 

North  of  the  falls  for  miles  nothing  but  granite  was  seen,  except 
where  this  rock  is  replaced  by  gneiss  and  is  cut  by  "doleritic"  and  other 
basic  dikes. 

Passing  to  the  green  schists  exposed  so  abundantly  on  the  Menominee 
River,  the  author  recoimts  their  occurrence  in  order,  beginning  vvith  the 
outcrops  at  Twin  Falls.  The  greenstone-schist  or  diorite  formation  is 
rarely  in  contact  with  the  iron  formation,  and  even  when  in  contact  the 
relations  between  the  two  rock  series  are  not  clearly  ascertainable. 


76  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

*  *  *  The  dioritic  rocks  generallj'  play  the  part  of  an  intrusive  rock  with 
regard  to  the  strictly  sedimentary  rock  beds  of  the  Huronian  series.  A  superposition 
of  the  diorite  formation  on  the  Lake  Hanbury  rock  series,  which  adjoins  it  the  whole 
length  of  the  Menominee  Valley  from  the  Upper  [Big]  Quinnesec  Falls  to  the  Stur- 
geon Falls,  asserted  by  Major  Brooks,  is  not  observable;  the  nearly  vertical  strata 
of  both  formations  are  even  never  seen  in  contact.  There  is  always  quite  a  large 
covered  interval  between  them.  The  nearest  exposures  of  the  two  groups  are 
observable  in  sec.  26,  T.  39,  R.  29,  where,  in  the  center  of  the  section,  a  hill  is 
foi'med  of  the  vertical  ledges  of  ferrugino-siliceous  flagstones  and  slaty  beds  repre- 
senting the  Lake  Hanbury  series,  and  about  two  or  three  hundred  steps  from  these 
exposures  we  find,  on  the  south  side  of  the  road  to  Menominee,  small  hillocks  of 
diorite.     *     *     * 

My  reasons  for  holding  the  dioritic  rocks  south  of  the  iron  formation  as  older 
than  the  latter  are  based  on  the  lithological  similaritj"  of  this  formation  with  the 
dioritic  gi'oup  of  the  Marquette  district,  and  on  the  degree  of  metamorphism 
exhibited  by  the  two  groups,  the  dioritic  and  the  iron-bearing.  In  the  great 
succession  of  strata  commencing  with  the  Hanbury  slate  group  and  upward,  we 
rarely  find  a  bed  so  much  altered  that  its  sedimentary  structure  is  altogether 
obsolesced,  and  the  majority  of  the  strata  shows  it  very  plain,  while  in  the  dioritic 
rocks,  considered  to  be  the  j^ounger,  a  stratified  structure  is  also  recognizable,  but 
not  one  of  these  thousands  of  feet  of  ledges  exhibits  its  original  sedimentary 
lamination  with  any  degree  of  distinctness  like  the  others;  they  have  evidently-  been 
transformed  undei'  coopei'ation  of  heat  and  partially  brought  into  a  plastic  condition. 
*  *  *  One  might  object:  If  the  diorites  are  the  older  beds,  why  don't  we  find 
them  just  as  well  developed  on  the  north  side  of  the  upheaved  beds,  between  the 
quartzite  and  the  granite?  The  sandy  and  conglomeratic  nature  of  manj^  of  the  strata 
of  the  quartzite  and  iron  formation  proves  them  to  be  shore  deposits,  while  the 
dioritic  group  consists  onh^  of  the  finer  material  of  deep-sea  deposits,  which  explains 
the  pojnt  in  question.  Moreover,  the  dioritic  rocks  are  not  altogether  missing  on 
the  north  side  of  the  ore  formation,  as  we  can  see  by  the  occurrence  of  the  6-mile- 
long  chain  of  diorite  extending  eastward  from  the  Twin  Falls.     *     *     * 

The  equal  dip  of  the  strata  to  the  south  in  these  adjoining  formations  is  not 
necessarily  proof  of  the  j'ounger  age  of  the  most  southern  beds.  The  whole 
succession  is  so  near  to  a  vertical  position  that  in  many  instances  it  has  been  left 
uncertain  which  way  thev  dip.  but  suppose  their  dip  is  conformable  to  the  south;  the 
upheaval  of  the  diorites  bj^  the  eruption  of  the  still  more  southern  granite  masses 
pushing  the  whole  incumbent  rock  series  north  until  all  tipped  over,  is  the  hypothesis 
by  which  I  explain  the  succession  of  beds  as  an  inverted  one,  the  seemingly  lowest 
beds  being  actually  the  youngest  [pp.  208-210]. 

The  author  describes  the  exposures  along  the  Menominee  River  in 
detail  as  fine-  and  coarse-grained  greenstone-schists,  micaceous  chlorite- 
schists,  light-colored,  grayish-green   porphyritic    schists    containing   well- 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  77 

formed  orthoclase  crystals,  inicaceo-feldspathic  seams,  and  beds  of  pale-red 
schists  composed  of  orthoclase,  hydroraica,  and  quartz,  etc.  At  the  Big 
Quinnesec  Falls  are  also  raas.sive  diorites.  These  and  the  diorite-schists 
have  the  same  composition,  and  neither,  according-  to  the  author,  should  be 
classed  with  the  diabases.  The  whole  series  of  rock  beds  exposed  at  these 
falls  "evidently  represents  one  inseparable  group  of  altered  sedimentary 
deposits  formed  from  bottom  to  top  of  the  same  material,  in  different 
molecular  form  and  different  proportion  in  the  intermixture  of  the 
component  mineral  substance"  (p.  214). 

The  rocks  at  the  Little  Quinnesec  Falls  and  at  the  Sturgeon  Falls  are 
similar  to  those  above  described.  Some  little  distance  below  the  mouth  of 
the  Sturgeon  River  are  said  to  be  exposures  of  serpentine,  and  below  these 
are  great  outcrops  of  feldspar,  porphyries,  granites,  etc.,  some  of  which  are 
thought  to  be  like  the  granite  and  porphyry  dikes  cutting  the  greenstone 
schists  of  the  "diorite  group"  in  the  Marquette  district. 

Reviewing  what  we  have  seen  of  the  formations  along  the  Menominee  River, 
said  to  be  the  youngest  of  the  Huronian  group,  I  again  point  out  the  great  similarity 
in  the  composition  and  structure  of  this  very  lai-ge  series  of  rocks  with  the  dioritic 
formation  of  the  Marquette  district;  also  its  intersection  bj'  the  serpentine  group, 
which  in  the  Marquette  district  is  under  similar  circumstances  associated  with  the 
diorite  formation.  Further  in  favor  of  this  analogy  is  the  intersection  of  the 
Menominee  diorites  by  porijhyritic  granite  in  dike  form,  as  is  the  case  with  the 
diorite  grovip  of  Marquette.  These  porphyritic  grahites  are  in  their  part  in  close 
relationship  with  the  felsite  porphyrj^  of  the  Pemenee  Falls,  merging  by  insensible 
gradations  with  the  granite,  which  is  only  a  more  completely  crystallized  form  of  the 
same  lava  mass.  On  the  other  hand,  there  exists  not  the  slightest  resemblance 
between  the  dioritic  rock  belt  of  the  Menominee  River  and  those  rock  beds  of  the 
Marquette  district  which  represent  subdivisions  15  to  20  of  Major  Brooks. 

The  exact  order  in  which  the  different  rock  masses  composing  the  dioritic  forma- 
tion succeed  each  other — whether  the  dark-green  diorites  of  the  Twin  Falls  and  in 
other  places  are  the  lowest  and  the  lighter-colored  diorites  at  the  Quinnesec  Falls 
the  higher  ones — is  at  the  present  state  of  our  knowledge  uncertain,  but  it  is  most 
likely  the  case;  so  the  dark-colored,  coarsely  crystalline  hornblende  rocks  exposed  a 
mile  above  the  Pemenee  Falls  may  be  older  beds  than  those  at  the  Quinnesec  Falls. 
The  massive  belts  of  this  series  of  altered  sedimentary  rocks,  interlaminated  with  the 
schistose  members,  can,  as  I  think,  not  all  be  considered  as  regular  links  in  the 
stratified  succession;  some  of  these,  and  particularly  the  larger  masses,  as  they  occur 
at  the  Quiver  Falls,  1  believe  to  be  intrusive,  in  the  same  qualified  sense  in  which  I 
have  considered  some  of  the  massive  dioritic  rock  belts  of  the  Marquette  district,  and 
still  in  another  sense  they  represent  only  a  more  altered  portion  of  the  stratified  beds 


78  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

connected  with  them.  Considering  the  g-ninite  on  the  soutli  and  west  side  of 
Menominee  Valley  as  an  eruptive  rock,  like  the  porphyiy  of  the  Pemenee  Falls,  1 
can  agree  full}'  with  Major  Brooks  in  this  part  of  his  chronological  system;  these 
rocks  undoubtedly  came  to  the  surface  after  all  the  other  Huronian  strata  of  sedi- 
mentary origin  were  formed,  as  their  eruption  to  the  surface  caused  the  upheaval  of 
the  others.  I  therefore  have  always  represented  the  dike  granites  of  the  Marquette 
district  as  actually  the  youngest  rocks  in  the  group,  but  I  suppose  this  was  not  the 
original  meaning  of  Major  Brooks's  system.  In  all  his  stratigraphical  descriptions 
he  has  not  made  a  proper  distinction  between  sedimentary  succession  and  interstrati- 
fication,  counting  up  the  beds  just  as  they  came  in  a  crosscut;  his  groups  VII,  IX, 
and  XI  are  a  proof  of  this  assertion  [pp.  221-222]. 

Ill  conclusidii  the  author  compares  the  rocks  of  the  Menominee  with 
those  of  the  Marquette  district,  all  of  which  are  reo^arded  as  Huronian  in  age. 

1883. 

Irving,  R.  D.  Iron  ores:  Geology  of  Wisconsin,  Survey  of  1873-1879.  vol.  1, 
pt.  3,  pp.  613-636.     1SS3. 

After  describing  in  general  the  iron  ores  found  in  Wisconsin,  Irving 
describes  briefly  the  geology  of  the  difierent  iron-ore  districts.  In  the 
Menominee  district  the  jjriucipal  Huronian  rocks  are  said  to  be  hornblendic 
and  micElceous  schists,  clay  slate,  chloritic  schist,  actiuolitic  schist,  limestone, 
diorite,  diabase,  and  iron  ore.  The  diorite  and  diabase  are  thought  by  the 
author  always  to  be  of  eruptive  origin,  and  to  occur  in  part  as  interbedded 
contemporaneous  flows  and  in  part  as  intrusions.  The  schists  are  intri- 
cately folded.  Any  mapping  of  the  folds  must  be  in  a  large  measure 
hypothetical,  because  of  the  numerous  faults  by  which  the  beds  are  crossed 
and  because  of  the  existence  in  them  of  masses  of  eruptive  material. 

The  ore  bodies  of  the  range  are  irregular,  lens-shaped  masses  or  portions  of  the 
belt  richer  than  the  rest.  These  lenses,  with  one  or  two  exceptions,  differ  from  most 
of  those  met  with  in  the  Marquette  region,  in  that  the  latter  are  distinctly  inter- 
calated, the  beds  above  and  below  them  closing  about  them,  while  in  this  case  the 
iron  oxide  simply  impregnates  certain  areas  of  the  stratum,  whose  subordinate  layers 
continue  undeflected  through  the  ore  bodies.  The  ores  are  of  the  peculiar  '"soft 
specular"  variety  already  noted  as  found  only  in  the  ^Menominee  region  [p.  621]. 

There  are  two  ore  horizons  in  the  district  according  to  Brooks,  the 
lower  of  which  was  numbered  VI  in  the  series.  This  is  the  horizon  on 
which  all  of  the  Michigan  mines  are  located.  The  second  horizon  is 
higher  in  the  series,  but  its  exact  position  Is  unknown. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  79 

On  a  later  page  in  the  same  article  several  analyses  of  Menominee 
ores  are  given,  most  of  them  being  copied  from  Wright's  report. 

Crednee,  H.     Eleniente  der  Geolog-ie,  pp.  400^10.     Leipzig.     1883. 

Credner  divides  the  pre-Gambrian  formations  into  the  Urgneiss  for- 
mation (the  Laurentian)  and  the  Ur-Schiefer  formation  (the  Huronian). 
In  the  latter  he  places  the  Menominee  rocks,  stating  that  the  dolomitic 
limestone  in  this  district  is  near  the  lower  limit  of  the  series.  He  gives  a 
section  across  the  district  from  north  to  sonth,  which  is  a  copy  from  his 
paper  on  this  district.  The  Ur  Schiefer  formation  in  the  Menominee,  as 
well  as  elsewhere,  is  unconformable  under  Lower  Silurian  sediments.  In 
this  district  the  iron  ore  is  overlain  in  places  by  sandstones  and  conglom- 
erates, which  are  found  sometimes  extending  down  into  cracks  in  the  ores. 
A  section  is  published  to  illustrate  this  relation.  A  few  other  references 
are  made  to  the  Menominee  rocks  in  the  author's  discussion  of  the  Archean, 
but  nothing  new  is  recorded  concerning  them. 

Ikving,  R.  D.  The  copper-bearing  rocks  of  Lake  Superior:  Mon.  U.  S.  GeoL 
Surve}' ,  vok  .5,  pp.  392-400,  with  maps,  including  a  general  map  of  the  Lake  Superior 
region.     1883. 

In  connection  with  his  discussion  of  the  Keweenawan  rocks,  Irving' 
briefly  describes  the  characteristics  of  the  lithology  of  the  Marquette  and 
of  the  Menominee  Huronian.  The  rocks  belonging  to  these  series  afford, 
at  first  glance,  a  strong  contrast  to  the  Penokee  Huronian.  Close  study, 
however,  shows  that  there  is  a  general  stratigraphical  equivalence  between 
the  three  series,  and  perhaps  even  a  direct  connection  between  them.  The 
author  compares  the  different  series  and  shows  their  points  of  resemblance 
and  of  difference.  The  diorites  of  the  Marquette  and  Menominee  regions 
he  suspects  to  be  altered  diabases.  The  granite  of  the  Menominee  district 
has  not  been  satisfactorily  shown  to  be  Huronian.  It  may  be  eruptive. 
Many  of  the  less  common  kinds  of  rocks  in  the  Marquette  and  Menominee 
districts  are  thought  to  be  due  to  metamorphic  changes,  which  may  be 
connected  with  the  complex  folding  observed. 

In  the  Menominee,  as  well  as  in  the  other  Huronian  areas,  the  Huronian 
schists  are  limited  by  granites  and  gneisses.  Usually  the  latter  rocks  are 
unconformably  beneath  the  schists  and  in  all  cases,  save  that  of  the  so-called 
Hiaronian   granite  in  the    Menominee  district  on  the  south  side  of   the 


80  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Meuomiuee  River,  the  granite  and  gneiss  complex  plainly  rises  from  beneath 
the  schists.  Most  of  the  crystalline  schists  associated  with  the  granites  and 
gneisses  are  older  than  the  Huronian  schists. 

1884.. 

WiNCHELL,  N.  H.     The  crystalline  rocks  of  the  Northwest:  Am.  Nat.,  vol.   18, 
pp.  984-1000.     1884. 

In  this  article  there  is  nothing  new  concerning  the  geology  of  the 
Menominee  district.  The  anther  simply  classes  all  the  crystalline  rocks  of 
the  Lake  Superior  region  into  six  groups  and  states  his  views  as  to  the 
equivalency  between  these  groups  and  those  established  by  other  w- iters 
on  the  different  crystalline  areas  of  the  Northwest,  among  which  is  included 
the  Menominee  area. 

Irving,  R.  D.,  and  Van  Hise,  C.  R.     On  secondary  enlargements  of  mineral 
fragments  in  certain  rocks:  Bull.  U.  S.  Geol.  Survey  No.  8,  p.  .39.     1885. 

One  of  the  specimens  described  by  the  authors  to  illustrate  their  con- 
tention that  fragments  of  minerals  in  clastic  rocks  are  often  enlarged  by 
the  deposition  of  secondary  material  around  them  is  from  the  bed  of 
Cambrian  sandstone  immediately  above  an  unconformable  contact  with 
Huronian  iron  ores  at  the  Cyclops  and  Norway  mines,  near  Norway,  in 
the  Menominee  district.     It  is  described  as — 

a  very  much  indurated,  buff  to  brown  sandstone — at  times  almost  a  vitreous  quartzite. 
The  thin  section  is  composed  almost  entirely  of  interlocking  grains  of  quartz  each 
with  its  distinctly  outlined  f  ragmental  core.  There  is  a  little  independently  deposited 
interstitial  quartz  and  a  little  f ragmental  feldspar. 

Whitney,  J.  D.,  and  Wadsworth,  M.  E.     The  Azoic  system  and  its  proposed 
subdivisions.     Bull.  Mus.  Comp.  Zool.  Harvard  College,  vol.  7,  pp.  xvi  and  331-565. 

1884. 

One  paragraph  in  this  volume  which  is  an  argument  in  favor  of  the 
indivisibility  of  the  pre-Cambrian  formations  criticises  Rominger's  views 
relating  to  Menominee  geology.     The  authors  declare  that  Rominger's — 

idea  that  the  Marquette  and  Menominee  schists  are  Huronian  means  nothing  beyond 
this,  that  the^'  appear  to  him  to  be  lithologically  similar  to  the  rocks  called  Huronian 
in  Canada;  while  so  far  as  his  actual  work  goes  he  reaches  conclusions  regarding  the 
relations  of  the  granitic  and  schistose  rocks  indentical  with  those  advocated  b}'  Foster 
and  Whitney  thirty  years  ago.  The  result  of  Rominger's  work  is  decidedlj'  opposed 
to  the  division  of  the  Michigan  Azoic  into  two  or  more  formations  [p.  494]. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  81 

1885. 

Swank,  James  M.     Iron  ores  in  the  United  States:  Mineral  Resoui'ces  U.  S.  for 

1883-84.     1885. « 

In  his  summary  description  of  the  iron-producing  districts  of  the 
United  States  the  author  declares  that  the  Menominee  district  ranks  second 
in  productiveness  to  the  Marquette  district.  About  1876  the  Menominee 
Mining  Company  of  Milwaukee  obtained  control  of  a  large  extent  of 
country  in  this  portion  of  Michigan  and  at  once  began  active  operation. 
In  1877  only  10,405  tons  of  ore  were  shipped,  but  thereafter  the  output 
increased  rapidly,  until  in  1882  it  rose  to  1,032,611  tons,  falling  in  1884  to 
698,047  tons.  The  Chapin  mine  was  the  largest  producer  in  the  entire 
Lake  Superior  region  in  1883  and  1884,  its  product  being  265,830  tons  in 
1883  and  290,972  tons  in  1884.  The  ores  are  generally  red  hematites, 
partaking  of  the  same  general  characteristics  as  the  similar  ores  of  the 
Marquette  district,  except  that  they  are,  as  a  rule,  softer.  Analyses  of 
specimens  of  ore  from  the  Vulcan,  Cyclops,  Norway,  and  Quinnesec  mines 
are  given  (pp.  265-266). 

Irving,  R.  D.  Preliminary  paper  on  an  investigation  of  the  Archean  formations 
of  the  Northwestern  States:  Fifth  Ann.  Rept.  U.  S.  Geol.  Survey,  pp.  175-242, 
with  general  map  of  Lake  Superior  region.     1885. 

The  problems  that  confront  the  investigator  of  the  ancient  rocks  of  the 
Lake  Superior  region  are  outlined  by  Irving  in  this  paper  and  the  progress 
made  in  solving  them  is  stated.  General  descriptions  are  given  of  the  series 
of  supposed  Huronian  rocks  in  the  different  areas,  among  them  descriptions 
of  those  occurring  in  the  Marquette  and  Menominee  areas,  which  are 
grouped  together. 

Their  rocks  are  highly  folded  and  their  structure  is  often  very  difficult  to  work 
out.  Moreover,  the  metasomatic  changes  which  the  crystalline  members  of  the  series 
have  undergone  have  often  been  extreme,  added  to  which  difficulties  are  fi-equent 
interruptions  by  drift  covering. 

«" Mineral  Resources  of  the  United  States"  has  been  published  annually  by  the  United  States 
Geologioal  Survey  since  1883.  Up  to  and  including  the  year  1894  it  appeared  as  an  independent  pub- 
lication. Later  it  was  published  as  part  of  the  "Annual  Report  of  the  Director,"  and  beginning  with 
the  year  1900  it  is  again  issued  as  an  independent  report.  It  contains  statistics  of  the  ore  production 
in  all  the  mining  districts  within  the  United  States  and  occasionally  descriptive  notes  concerning 
these  districts.  In  this  monograph  only  those  volumes  will  be  referred  to  which  contain  new  infor- 
mation of  geological  interest  concerning  the  Menominee  district. 

MON    XLVI — 04 6 


82  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  greenstone-schists  and  the  greenstones  at  the  Big  Quinnesec  and 
the  Little  Quinnesec  Falls  are  believed  to  be  eruptive,  the  schists  "repre- 
senting merely  an  extreme  degree  of  metasomatic  change,  which  in  some 
ineasure  has  influenced  all  the  greenstones." 

While  declining  to  acknowledge  the  possibility  of  establishing  a 
scheme  of  stratigraphy  for  these  districts  without  the  aid  of  good  maps, 
Irving  thinks  that  there  is  no  question  that  Brooks's  scheme  is  faulty  with 
respect  to  the  various  greenstone  layers  included  among  the  sedimentary 
beds.  These  greenstones  -are  believed  by  Irving  to  be  altered  basic 
eruptives,  some  of  which  are  contemporaneous  flows,  and  others  intrusive 
masses.  The  jaspers  and  ores  of  the  Menominee,  like  those  of  the  Marquette 
district,  are  believed  to  be  of  sedimentary  origin.  In  the  Menominee  district 
much  of  the  silica  in  the  jaspers  is  chalcedonic,  and  many  great  belts  of 
ferruginous  rocks  seem  to  be  mainly  composed  of  it.  The  Menominee  area 
is  thought  to  connect  westward  with  the  area  of  the  upper  Wisconsin  Valley, 
but  detailed  mapping  of  this  westward  extension  had  not  been  completed 
when  the  author  wrote  his  paper. 

One  plate  in  the  report  illustrates  an  unconformity  between  the  Ores 
and  the  Potsdam  sandstone  at  the  Cyclops  mine,  Norway. 

In  the  petrograi)liical  portion  of  the  paper  the  author  refers  to  the 
existence  in  the  Menominee  district  of  clay  slates,  some  of  which  are  fine- 
grained graywackes  in  which  the  feldspathic  ingredients  are  largely 
represented  by  kaolinized  material,  while  others  present  distinct  gradations 
into  true  mica-slates  and  mica-schists,  in  which  at  least  a  considerable 
proportion  of  the  material  is  of  original  crystallization.  Other  rocks  are 
also  described,  but  only  the  limestones  are  referred  to  as  existing  in  the 
Menominee  district  proper.  The  cherts,  however,  are  mentioned  as  being 
in  part  at  least  of  direct  chemical  origin.  All  the  quartzites  in  the  Huronian 
are  thought  to  be — 

merely  sandstones  which  have  received  various  degrees  of  induration  by  the 
interstitial  deposition  of  a  siliceous  cement,  which  has  generally  taken  the  form  of 
enlargements  of  the  original  quartz  fragments,  less  corpmonly  of  minute  independently 
oriented  areas,  and  still  less  commonly  of  an  amorphous  or  chalcedonic  silica,  two  or 
even  all  three  forms  of  the  cementing  silica  occurring  at  times  together  in  the  same 
rock  *  *  *.  It  appears  that  they  have  undergone  no  other  alteration  than  that 
found  to  affect  sandstones  in  the  newer,  undisturbed,  and  generally  unaltered 
formations  [p.  236]. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  83 

1886. 

Ikving,  R.  D.  Origin  of  the  ferruginous  schists  and  iron  ores  of  the  Lake 
Superior  region:  Am.  Jour.  Sci.,  3d  series,  vol.  32,  pp.  255-278.     1886. 

Althoug'h  the  argument  in  this  paper  is  based  particularly  on  observa- 
tions made  in  other  districts,  the  author,  nevertheless,  refers  to  the  Menom- 
inee ores  as  having  resulted  from  the  alteration  of  an  iron  carbonate  whose 
origin  was  sedimentary.  The  Menominee  rocks  are  much  folded,  like  those 
of  the  Marquette  region,  and  in  them  the  alteration  of  the  carbonate  has 
proceeded  much  further  than  in  the  unfolded  series  of  the  Penokee  and 
other  districts.  In  these  districts  all  the  phases  of  the  altered  carbonates 
are  met  with,  but  the  quantity  of  unaltered  material  is  much  less  than  it  is 
in  the  less  folded  rocks.  The  j^rocess  by  which  the  alteration  has  been 
effected  and  the  proof  that  this  alteration  is  responsible  for  the  existence  of 
the  ores  need  not  be  referred  to  In  this  place.  An  account  of  these  discus- 
sions is  given  in  the  literature  chapter  of  the  Marquette  monograph." 

The  author  refers  to  the  Menominee  iron-bearing  series  as  being  so 
folded  that  the  rock  belts  for  the  most  part  are  in  an  approximately  vertical 
position.  The  most  abundant  of  the  ferruginous  rocks  are  cherty  schists 
charged  with  varying  quantities  of  magnetite,  hematite,  and  brown  oxide  of 
h'on,  and  containing  more  or  less  iron  carbonate.  These  schists  graduate 
into  graphitic  and  carbonaceous  slates  that  are  sometimes  highly  contorted 
and  at  other  times  are  nearly  free  from  contortions. 

These  contortions  have  no  parallel  in  the  adjoining  layers,  and  often  seem  to 
have  little  relation,  in  axial  directions,  to  the  general  system  of  folding  of  the  strata. 
They  are  taken  to  indicate  the  relatively  great  resistance  to  folding  offered  by 
these  schists,  on  account  of  the  siliceous  induration  they  received  prior  to  the  folding 
process  [p.  265J. 

The  iron  carbonate  occurs  in  the  schists  as  an  original  ingredient  in 
varying  proportions.  Actinolite  is  present  in  some  of  them.  The  siliceous 
matter  in  them  is  more  commonly  cherty  or  flinty  than  jaspery,  but  at 
times  it  is  jaspery  over  large  areas.  The  iron  ores  lie  in  these  schists,  not 
as  lens-shaped  masses  around  which  the  schists  bend,  but  as  irregular 
bodies  lying  directly  in  the  course  of  the  schistose  banding  or  as  layers 
within  the  schists.     The  ores  appear  to  have  originated  in  one  of  two  ways, 

« Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897,  pp.  5-148. 


84  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

or  in  a  combination  of  them,  viz,  from  direct  oxidation  of  the  bauds  of  car- 
bonate in  place,  and  from  deposition  within  the  schist  of  oxide  of  iron  from 
percolating  waters.  All  the  indications  point  to  the  derivation  of  both  fer- 
ruginous rocks  and  iron  deposits  by  a  process  of  silicification  from  stratiform 
shales  impregnated  with  carbon  and  iron  carbonate. 

PuMPELLY,  R.     Report  on  the  uaining  industries  of  the  United  States  (exclusive 
of  the   precious   metals),   etc.     Rept.  Tenth   Census   U.   S.,  vol.  15.     With  maps. 

1886. 

Putnam,  Batard  T.     Notes  on  the  samples  of  iron  ore   collected  in  Michigan 
and  northern  Wisconsin,     Rept.  Tenth  Census  U.  S.,  vol.  15,  p.  421.     1886. 

In  his  introduction  to  the  discussion  of  analyses  of  Menominee  iron 
ores  Putnam  gives  a  brief  outline  of  the  geology  of  the  Menominee  district. 
He  recognizes  two  belts  of  iron-bearing  rocks,  as  did  Brooks  before  him. 
The  Southern  belt  embraces  the  region  now  known  as  the  Menominee 
district.  Since  the  completion  of  the  Chicago  and  Northwestern  Railway 
to  Quinnesec  in  1877  the  mines  on  the  eastern  portion  of  the  Southern  belt 
have  been  extensively  wrought,  yielding,  as  Pumpelly  declares  in  his 
introduction  to  the  general  discussion  of  the  iron  ores,  491,347  tons  during 
the  census  year  1880.     The  ores  consist — 

principally  of  a  soft,  specular,  blue  hematite,  which  runs  high  in  iron  and  low  in 
phosphorus.  Although  quite  soft,  the  ore  usually  resists  hydration  and  rarely 
changes  color  except  in  handling.  *  *  *  When  examined  fresh  from  the  mine 
the  ore  is  seen  to  be  made  up  of  innumerable  fine  crystalline  particles  of  specular 
hematite,  which  are  somewhat  loosely  agglutinated.  *  *  *  The  ore  usually 
occurs  in  irregular  pockets  or  lens-shaped  masses  in  a  banded  quartzose  ferruginous 
schist,  which  is  often  magnetic  [p.  437]. 

Sketch  maps  of  the  Emmett  and  Breen  mines,  of  the  Vulcan,  the  East 
Vulcan,  the  Curry,  the  Saginaw  and  Stephenson,  the  Norway,  the  Quinne- 
sec, the  Chapin,  the  Ludington,  and  the  Cornell  mines,  and  sections  through 
many  of  them,  illustrate  the  paper.  At  the  Emmett  mine  the  ores  consist  of 
an  upper  blue  variety  and  a  lower  brown  variety,  both  of  which  dip  south- 
ward under  a  swamp.  The  blue  ore  is  protected  from  the  action  of  the 
swamp  water  by  a  covering  of  clay,  while  the  brown  oi'e  is  saturated  with 
ground  water  which  nses  through  the  underlying  schist.  The  blue  ore 
contains  but  0.008  per  cent  of  phosphorus,  while  the  brown  ore  contains 
0.103   per  cent  of  this  element.     At  the  Vulcan  mine  the  ore  lens  dips 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  85 

south  and  pitches  west.  One  of  the  ore  samples  from  this  mine  contains  a 
small  proportion  of  titanium,  thus  proving  an  exception  to  the  Menominee 
ores  in  general,  which  are  usually  free  from  this  metal.  In  one  of  the  pits 
of  this  mine  the  ore  is  overlain  by  a  ferruginous  siliceous  schist,  which  is 
so  richly  impregnated  with  iron  near  the  ore  body  that  it  sometimes  itself 
constitutes  a  lean  ore.  At  the  Norway  mine  the  ore  is  between  a  foot  wall 
of  soap  rock  and  a  hanging  wall  of  "conglomerate  ore,"  composed  of  irreg- 
ular angular  pieces  of  hard  specular  ore  cemented  by  soft  brown  hematite. 

1887, 

BiRKiNBiNE,  John.  The  iron  ores  east  of  the  Mississippi  River:  Mineral 
Resources  U.  S.  for  1886,  pp.  65-67.     1887. 

The  author  gives  a  biief  history  of  the  operations  in  the  Menominee 
district  since  1877,  describes  the  work  done  at  the  Hamilton  mine,  and 
furnishes  the  usual  statistics  of  the  output  of  the  principal  mines  on  the 
range  as  well  as  of  the  district  as  a  whole. 

Irving,  R.  D.  Is  there  a  Huronian  group?  Am.  Jour.  Sci.,  3d  series,  vol.  34, 
pp.  204-216,  249-263,  and  365-374.     1887. 

In  this  article  Professor  Irving  gives  his  reasons  for  regarding  the  series 
of  nonfossiliferous  sediments  lying  between  the  top  of  the  Archean  crystal- 
line schists  and  the  bottom  of  the  Potsdam  sandstone  in  the  Lake  Superior 
region  as  worthy  of  being  considered  a  distinct  system  coordinate  in 
importance  with  the  Paleozoic,  etc.,  with  the  Huronian  as  a  distinct  group 
in  the  system.  The  arguments  made  use  of  have  been  outlined  in  the 
Marquette  monograph."  In  his  description  of  a  section  through  the  Menomi- 
nee district,  the  author  declares  that  the  chief  difference  existing  between 
the  Marquette  and  the  Menominee  rocks  lies  in  the  much  closer  folding  of 
the  latter.  All  the  arguments  that  apply  in  favor  of  the  existence  of  the 
two  formations  in  the  Marquette  district  apply  also  in  the  Menominee 
district.  A  more  detailed  elaboration  of  the  arguments  is  given  in  the  paper 
on  the  classification  of  the  pre-Cambrian  formations,  referred  to  below. 

1888. 

Irving,  R.  D.  On  the  classification  of  the  early  Cambrian  and  pre-Cambrian 
formations;  a  brief  discussion  of  j^rinciples,  ilhistrated  by  examples  drawn  mainly 
from  the  Lake  Superior  region:  Seventh  Ann.  Rept.  U.  S.  Geol.  Survey,  pp.  365-454. 
With  maps,  including  a  general  map  of  the  Lake  Superior  region.     1888. 

"Moil.  U.  S.  Geol.  Survey,  vol.  28,  1897,  pp.  110-112. 


86  THE  MENOxMINEE  IRON-BEARING  DISTRICT. 

The  main  portion  of  this  paper  is  a  discussion  of  the  value  of  uncon- 
formities in  classifying  nonfossiliferous  sedimentary  beds.  The  illustrations 
taken  from  the  Lake  Superior  region  afford  examples  of  great  unconformities 
in  all  the  areas  that  have  been  recognized  as  Huronian. 

In  the  Menominee  district  there  are  many  outliers  of  the  Potsdam  sand- 
stone reposing  horizontally  on  the  upturned  edges  of  the  Huronian  schists. 
A  picture  (p.  410)  illustrates  the  appearance  of  a  contact  of  sandstone  on 
the  steeply  inclined  beds  of  the  iron-bearing  schists  near  Norway.  At  the 
immediate  contact  of  the  two  series  the  sandstone  is  filled  with  fragments  of 
the  schists.  The  iron-bearing  rocks  are  thus  demonstrably  older  than  the 
sandstones. 

Beneath  the  Huronian  is  another  series  of  rocks,  comprising  granites, 
gneisses,  and  hornblendic  and  micaceous  schists.  These  rocks  are  closely 
folded,  and  upon  them,  in  eroded  basins,  the  Huronian  schists  are  deposited. 
The  upper  series  is  a  relatively  little-altered  iron-bearing  series  and  the 
lower  one  a  deeply  altered  series  of  gneiss  and  schists,  cut  by  immense 
masses  of  intnisive  granite.  There  is  evidently  a  great  discordance  between 
the  two  series — a  discordance  that  is  further  marked  by  the  existence  of  a 
great  basal  conglomerate  at  the  Falls  of  the  Sturgeon  River.  The  folding  in 
this  district  is  often  so  sharp  that  there  is  a  seeming  conformity  between  the 
upper  and  the  lower  series  in  many  places.  A  generalized  cross  section  of 
the  Menominee  rocks  in  the  vicinity  of  Quinnesec  illustrates  the  author's 
interpretation  of  the  geology  of  the  district  (p.  435). 

Larsson,  Per.  The  Chapin  iron  mine,  Lake  Superior:  Trans.  Am.  Inst.  Min. 
Eng.,  vol.  16,  pp.  119-128.     Map  and  cross  sections.     1888. 

Larsson's  article  is  devoted  mainly  to  a  description  of  the  methods 
employed  in  mining  at  the  Chapin  mine,  although  in  its  introduction  brief 
reference  is  made  to  the  geology  of  its  ore  deposits.  Up  to  July,  1887,  the 
ore  of  this  mine  had  been  found  in  three  lenses,  conforming  in  dip  and 
strike  with  the  Huronian  clay  slates  and  jaspers  associated  with  them,  and 
pitching  about  30°  west. 

A  cross  section  of  the  ore  formation  shows  on  the  north  or  hanging  side  of  the 
ore  about  200  feet  of  clay  slates,  and  farther  north  a  heavy  belt  of  magnesian 
limestone.  The  slates  and  the  dolomite  are  generally  separated  by  a  conglomerate 
of  broken  dolomite  and  soft  slates. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  87 

The  foot-wall  rock  is  also  a  soft  slate,  containing  a  higher  percentage  of  iron 
and  less  magnesia  than  the  hanging  slate.  Farther  south  occur  alternate  beds  of 
slates  and  lean  ore  or  jasper  [p.  119]. 

The  paper  is  accompanied  by  a  geological  map  of  the  Chapin  mine 
property,  a  longitudinal  section  of  the  workings,  and  two  cross  sections 
exhibiting  the  geological  relations  between  ore,  slate,  and  dolomite. 

Fulton,  John.  Mode  of  deposition  of  the  iron  ores  of  the  Menominee  ii-on 
range,  Michigan:   Trans.  Am.  Inst.  Min.  Eng.,  vol.  16,  pp.  525-536,  with  9  figures. 

1888. 

According  to  this  author  the  Menominee  range  is  composed  of  three 
distinct  groups  of  Huronian  rocks.  The  "supporting  group"  consists  of 
1,200  feet  of  light-colored,  siliceous  limestones,  called  the  Norway  limestone 
belt. 

The  next  or  flanking  group  which  is  estimated  at  a  thickness  of  1,000  feet  is 
called  the  Quinnesec  ore  formation.  It  consists,  in  the  portion  next  to  the  lime- 
stone, of  siliceous  or  jasper  slates,  largely  impregnated  with  iron  oxide.  These  ai-e 
succeeded  by  argillaceous  hydro-mica  black  and  flesh-colored  slates.  This  formation 
embraces  the  deposits  of  the  iron  oi*es. 

The  third  group  consists  of  a  series  of  dark-gray,  slaty,  or  schistose  beds,  with 
occasional  quartzose  bands,  having  a  thickness  of  2,000  feet.  It  is  called  the  Lake 
Hanbury  slate  group  [p.  525]. 

The  three  groups  succeed  one  another  conformably,  dipping  at  high 
angles  to  the  south  in  that  portion  of  the  range  east  of  Quinnesec  and  to  the 
north  in  that  portion  west  of  this  town.  Their  relative  ages  can  not  be 
determined  from  their  relative  positions,  as  "the  limestone  is  the  floor  of 
the  series  east  of  Quinnesec,  while  west  of  this  it  is  uppermost"  (p.  527). 
There  is  a  well-marked  unconformity  between  the  Huronian  rocks  and  the 
overlying  Potsdam  sandstone,  but  the  geology  of  the  older  rocks  is  com- 
plicated by  "frequent  and  violent  flexures  and  strangely  postured  dips" 
(p.  527). 

The  rocks  of  the  three  groups  are  sedimentary.  The  iron  ore  at  the 
Quinnesec  mine  is  thin  bedded,  as  are  also  the  foot-wall  jasper  slates. 
The  limestone  is  thick  bedded.  The  ore  occurs  at  two  or  three  hori- 
zons, which,  so  far  as  is  known,  are  not  constant.  At  the  East  Vulcan 
mine  one  of  the  ore  bodies  is  at  the  contact  between  the  siliceous  or  jasper 
slates  and  the  aluminous  slates  or  "soapstone."  A  second  is  in  jaspers 
south  of  the  black  slates.     At  the  Curry  mines  there  are  also  two  horizons 


88  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

at  Avhich  the  ore  occurs.     The  fii-st,  most  northerly,  is  in  jasper  slates  and 
the  second  at  the  contact  between  the  jasper  and  black  slates. 

The  Norway  deposit  is  pecuHar,  being  separated  from  the  Umestone  by  about 
10  to  40  feet  of  brown  sediment,  locally  termed  "soap  rocli."  The  ore  body  is 
mainly  composed  of  a  brecciated  deposit  of  red  and  blue  iron  ore,  occasionallymixed 
with  jasper  slates,  and  cemented  in  great  masses  [p.  531]. 

The  underground  workings  reveal  the  existence  of  a  fold  in  the 
limestone. 

The  large  open  pits  of  C\'clops  are  very  peculiar,  as  they  are  the  residuum 
of  a  period  of  denudation  and  destruction  of  the  ore  body.  These  pits  occur  in  the 
jasper  slates,  without  any  regularity.  *  *  *  The  ore  was  evidently  carried  into 
them  by  some  eroding  current  from  the  wreck  of  an  original  deposit.  Just  where 
it  came  from,  or  under  what  conditions  it  was  swashed  into  these  large  pits  can  not 
be  determined.  *  *  *  The  example  of  a  pool  of  ore  at  East  Vulcan  illustrates 
the  supposed  condition  of  these  Cyclops  deposits  [p.  532]. 

At  the  Quinnesec  mine  a  similar  "pool"  of  ore  is  found  infolded  in 
the  Potsdam  sandstone.  A  little  east  of  this  mine  a  flexure  occurs  in  the 
Huronian  rocks,  west  of  which  fold  the  beds  dip  north. 

The  blue  ores  of  the  Quinnesec  and  of  the  West  Vulcan  mines  are 
in  the  form  of  lenses  whose  tops  have  been  eroded.  These  are  thought  to 
represent  the  original  form  in  which  all  the  ore  in  the  range  once  occurred. 
They  are  embedded  in  jasper  and  clay  slates,  and  are  stratified  like  these 
rocks. 

After  thus  describing  the  characteristics  of  many  of  the  deposits  the 
author  proceeds  to  outline  a  theory  to  explain  their  origin. 

The  most  acceptable  exposition  indicates  that  their  normal  form  was  that  of 
thinly  bedded  ferriferous  carbonates,  with  some  admixture  of  dusty  magnetite,  and 
that  they  have  been  wholly  altered  to  hematite  by  heat  in  their  lower  geological 
horizon,  together  with  the  heat  evolved  in  the  pitching  and  folding  of  the  rock- 
measures  in  which  they  are  found.  Chemical  agencies  also  contributed  to  this  result 
[p.  535]. 

The  author  concludes  by  declaring  that  the  structure  of  the  range  can 
not  be  explained  as  "a  continuous  monocliual  structure."  "The  more 
evident  structure  should  consist  of  a  series  of  crust  flexures,  repeating  the 
iron-ore  measures  at  intervals,  as  they  rise  on  the  crests  or  flanks  of 
anticlinal  waves"  (p.  536). 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  89 

The  papei"  is  accompanied  by  a  map  of  the  district  and  nine  geological 
sections  through  mines. 

Fulton,  John.  Methods  of  mining  in  the  Menominee  range,  Michigan:  Trans. 
Am.  Inst.  Min.  Eng.,  vol.  16,  pp.  891-906,  with  8  figures.     1888. 

The  introductory  portion  of  this  paper  describes  the  position  of  the 
ore  bodies  with  respect  to  the  jaspers  and  slates  in  the  Menominee  district. 
These  ore  bodies  are  reported  as  being  found  in  three  or  more  horizons  in 
the  jasper  slates  and  also  on  the  contact  between  these  and  the  clay  slates 
that  usually  overlie  them.  The  remainder  of  the  paper  is  devoted  to  a 
description  of  the  methods  of  mining  on  the  range. 

1889. 

Lawton,  Chas.  D.     Mineral  resources  of  Michigan,  1888,  pp.  190-208.     1889. 

In  this  report  on  the  mines  and  mineral  resources  of  Michigan  the 
author  announces  the  discovery  of  a  large  percentage  of  gold  in  the  rock 
from  a  pit  near  the  bank  of  the  Menominee  River,  south  of  Quinnesec. 
He  also  gives  an  account  of  the  condition  of  the  iron  mines  on  the 
Menominee  range  at  the  close  of  the  year  1888.  In  his  introduction  to 
that  part  of  the  paper  which  deals  with  the  Menominee  district  he  outlines 
the  geology  of  the  district  as  worked  out  by  Brooks. 

WiNCHELL,  N.  H.,  and  Winchell,  H.  V.  On  a  possible  chemical  origin  of  the 
iron  ores  of  the  Keewatin  in  Minnesota:  Proc.  Am.  Assoc.  Adv.  Sci.,  Thirty-eighth 
Meeting,  pp.  235-242.     1889.     Also  Am.  Geologist,  vol.  4,  pp.  291-300.     1889. 

Although  this  paper  is  devoted  mainly  to  a  theorj^  in  explanation  of 
the  origin  of  the  iron  ores  in  Minnesota,  Professor  Winchell  nevertheless 
argues  against  Irving's  view  that  the  ores  of  all  the  iron-ore  districts  in 
Michigan  and  Wisconsin  are  derived  by  metamorphic  processes  from  an 
iron  carbonate. 

Browne,  D.  H.  The  distribution  of  phosphorus  in  the  Ludington  mine.  Iron 
Mountain,  Michigan:  Am.  Jour.  Sci.,  3d  series,  vol.  37,  pages  i!99-310,  with  figures. 

1889. 

The  ore  of  the  Ludington  mine  occurs  in  several  lenses  lying  in  clay 
slates.  The  main  deposit,  which  is  700  feet  long  and  about  60  feet  wide, 
strikes  N.  75°  W.  and  pitches  45°  W.  Its  dip  is  70°  to  80°  N.  The  ore 
is  of  a  soft,  laminated  hematite,  whose  layers  alternate  in  places  with  thin 
seams  of  calcium-magnesium   carbonate.     The   contact  of  the    ore    body 


90  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

with  the  hanging  wall  is  curved,  while  that  with  the  foot  wall  is  more 
nearly  a  plane  surface.  Upon  mapping  the  phosphorus  contents  of  the 
different  samples  of  ore  taken  from  the  mine  it  was  found  that  the  foot- wall 
sides  of  the  deposits  are  apt  to  contain  less  phosphorus  than  the  hanging- 
wall  sides,  and  that  the  western  (lower)  ends  of  the  lenses  contain  less 
phosphorus  than  the  eastern  (upper)  ends.  The  ore  increases  in  phos- 
phorus from  the  foot  wall  to  the  hanging  wall,  and  from  the  west  to  the 
east.  Sometimes  a  streak  of  ore  rich  in  phosphorus  crosses  the  high-grade 
ore,  but  in  general  the  relations  just  mentioned  obtain.  These  relations 
are  illustrated  in  the  paper  by  a  large  number  of  sections  through  the 
different  rooms  in  the  mine  from  which  ore  has  been  removed. 

The  explanation  offered  to  account  for  the  regularity  in  the  distribu- 
tion of  the  phosphorus  is  as  follows:  The  ores  were  aqueous  deposits  upon 
the  hanging-wall  slates. 

If  we  suppose  that  the  ore  was  formed  in  hollows  in  the  hanging  wall,  and  was 
covered  by  the  foot-wall  slates,  and  that  this  bed  has  been  tilted  up  from  the  north 
side  through  an  angle  of  100°  to  110°,  it  will  be  readily'  understood  that  the  original 
trend  of  the  deposit  becomes  the  complement  of  the  present  pitch  of  the  ore.  This 
supposition  exi^lains  *  *  *  the  fact  that  what  is  now  the  hanging  wall  seems  to 
have  been  the  original  bed  of  the  deposit.  It  is  improbable  that  the  tilting  has  been 
from  the  south  side  upward  through  an  angle  of  70°  to  80°;  for  if  this  had  been  the 
case  the  ore  would  pitch  east  at  the  same  angle  at  which  it  now  pitches  west  [p.  306]. 

The  author  does  not  think  that  Van  Rise's  explanation  of  the  origin 
of  the  ores  in  the  Gogebic  district  can  be  applied  to  the  conditions  in  the 
Menominee  district,  because  the  slates  associated  with  the  Menominee  ores 
contain  no  unaltered  carbonate.  The  suggestion  of  Irving  that  the  ore 
was  washed  into  its  present  position  from  previously  precipitated  beds  of 
carbonate  appears  to  him  more  plausible,  but  he  would  modify  the  theory 
by  making  the  original  deposits  hydrous  oxides  and  carbonates  of  iron 
intermixed  with  calcareous  materials.  By  the  action  of  acidulated  waters 
upon  these  the  iron  was  dissolved  and  the  solutions  thus  formed  were 
evaporated  in  shallow  lakes  or  valleys,  yielding  the  ore  deposits  now 
worked. 

The  theory  of  the  aqueous  deposit  of  these  ore  bodies,  as  drawn  from  chemical 
evidence,  is  then  briefly  as  follows:  From  previously  deposited  beds  of  bog  iron  ore, 
by  the  action  of  acidulated  water,  iron,  lime,  silica,  and  phosphorus  were  dissolved. 
The  first  solution  contained  a  large  amount  of  phosphorus  in  propoition  to  the 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  91 

amount  of  iron  dissolved.  On  coming  into  hollows  in  the  surface  of  the  exposed 
slates  the  acid  solution,  losing  acid  by  evaporation,  deposited  iron,  as  hydrated  oxide, 
which  carried  down  an  amount  of  phosphorus  proportionate  to  the  amount  of  iron 
precipitated.  As  the  acid  became  still  weaker  crystals  of  carbonate  of  lime  and 
magnesia  settled  out,  forming  a  layer  of  carbonates.  A  second  inflow  of  water  would 
tend  to  dissolve  these  crystals  and  precipitate  another  layer  of  iron.  In  similar  man- 
ner, by  successive  inundations,  the  depressions  became  filled  with  alternating  layers  of 
iron  ore  and  calcium-magnesium  carbonates,  each  laj'er  being  as  a  rule  lower  in  phos- 
phorus than  the  preceding  one.  *  *  *  Moreover,  as  both  calcium  and  iron  phos- 
phate are  of  lower  specific  gravity,  and  more  soluble  than  the  hydrated  oxide  of  iron, 
the  tendency  of  the  water  was  to  carry  these  phosphates  toward  the  lower  end  of  the 
lake,  and  to  deposit  them  in  shallow  water,  along  banks  of  previously  precipitated  silica 
and  in  places  where  precipitation  was  most  rapid.  *  *  *  After  the  deposition  was 
complete,  further  action  of  the  water  would  stir  up  the  upper  layers  of  ore  and  mix 
them  with  suspended  sand  or  clay,  while  the  iron  and  phosphorus  were  carried  farther 
along,  to  be  deposited  in  other  depressions  to  the  northeast.  As  jasper  occurs  as  vein 
matter,  and  in  lamint«  cleaving  in  the  same  line  as  the  ore,  it  would  seem  either  that 
the  jasper  has  been  produced  by  precipitation  with  the  iron,  or  that  subsequent  action 
of  water  has  eroded  the  beds  of  iron  thus  formed  and  substituted  silica  for  the  iron 
removed. 

A  study  of  the  vein  map  of  the  sixth  level  at  the  Ludington  mine  *  *  * 
seems  to  show  that  the  jasper  is  a  later  formation  than  the  ore.  It  will  be  seen 
by  reference  to  fig.  17  [figure  22  in  the  article]  that  the  jasper  deposit  widens  toward 
the  foot  wall.  *  *  *  The  greater  width  of  the  jasper  at  the  foot  wall  also  sug- 
gests an  erosion  of  the  original  ore  bed  and  a  subsequent  deposition  of  silica.  Had 
the  silica  been  the  primary  deposit  the  ore  would  be  widest  at  the  foot  wall  instead 
of  at  the  hanging  [pp.  307-308]. 

For  the  explanation  of  the  silica  deposits  "bedded  in  the  same  plane 
with  the  ore,"  the  author  adopts  Van  Hise's  hypothesis,  "with  the  provision 
that  subsequent  erosion  must  be  taken  into  consideration."  The  "surface 
deposits  or  washes  of  ore  formed  at  Keel  Ridge,  Quinnesec,  and  Norway 
mines"  are  thought  to  be  accumulations  of  the  detritus  worn  away  from 
outcropping  edges  of  ore  dui'ing  the  glacial  erosion.  After  the  deposition 
of  the  ore  it  was  greatly  modified  in  its  chemical  peculiarities  by  the  action 
of  surface  water,  removing  phosphorus  in  one  place  and  adding  it  in 
another. 

The  theory  of  aqueous  deposit  will  explain,  as  will  no  other,  the  marked  regu- 
larity of  isochemic  lines  [lines  drawn  through  those  portions  of  the  deposit  containing 
equal  quantities  of  phosphorus]  and  their  peculiar  curves,  the  regular  decrease  of 
phosphorus  from  hanging  wall  to  foot,  the  alternation  of  carbonate  of  lime  and  oxide 


92  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

of  iron,  the  ripple-marked  hanging  wall,  the  uniform  lamination  of  the  oi-e,  and 

the  hydrated  muddj"-  deposit  next  the  foot  wall.     It  also  suggests  explanation  of 

the  general  features  of  the  Menominee  range,  and  the  gradual  change  from  high 

phosphorus  and  low  iron  ores  resembling  altered  bog  ores  at  its  western  extremity, 

through  regular  deposits  of  high  iron  and  lower  phosphorus,  to  the  immense  washes 

and  surface  deposits  of  exceedinglj^  low   phosphorus  ore  which  mark  its  eastern 

termination  (p.  309). 

1890. 

Irving,  R.  D.  The  greenstone  schist  areas  of  the  Menominee  and  Marquette 
regions  of  Michigan;  explanatory  and  historical  notes:  Bull.  U.  S.  Geol.  Survey  No. 
62,  pp.  11-30.     Map  of  Menominee  district  opp.  p.  24.     1890. 

In  this  introductory  note  to  Dr.  Williams's  study  of  the  greenstone- 
schists  of  the  Marquette  and  Menominee  districts  Irving  gives  an  historical 
summary  of  the  views  held  by  his  predecessors  with  respect  to  the  relations 
existing  between  these  schists  and  the  bedded  sedimentary  rocks  associated 
with  them.  The  general  problems  connected  with  the  subject  have  been 
outlined  in  the  Marquette  monograph."  These  green  schists  occur  inter- 
mingled with  granites  and  also  form  large  continuous  areas,  which  they 
entirely  occupy,  except  for  some  unimportant  dikes  that  intrude  them. 
Some  of  these  I'ocks  are  now  hornblende-schists,  others  are  c^dorite- 
schists,  wdiile  still  others  are  massive  greenstones.  In  the  Menominee 
district  the  schists  occur  south  of  the  ore  belt.  They  are  well  exposed  at 
the  Big  and  the  Little  Quinuesec  Falls  and  at  the  Sturgeon  Falls  on 
the  Menominee  River,  and  again  in  the  vicinity  of  the  Fourfoot  Falls, 
north  of  Bass  Lake.  These  schists,  it  will  be  i-emembered,  were  regarded 
by  both  Brooks  and  Rominger  as  layers  of  sedimentary  material  that 
have  been  metamorphosed  since  their  deposition.  By  Brooks  they  were 
considered  to  be  the  uppermost  beds  of  the  Huronian  series  and  by 
Rominger  as  the  basal  layers  of  this  system.  To  Irving  the  regularity  of 
the  alternations  in  the  schists  seems  less  than  one  would  think  to  be  the  case 
from  Brooks's  maps.  The  rocks  seemed  to  him  to  grade  into  one  another 
and  into  the  massive  beds.  The  schistosity  appears  to  be  of  secondary 
orisrin  and  the  orig-inal  structure  of  the  rocks  seems  to  have  been  massive. 
In  the  Menominee  district  a  series  of  detrital  iron-bearing  rocks  lies  between 
the  green  schists  and  great  areas  of  granite  and  gneiss  to  the  north.  The 
iron-bearing  rocks  are  similar  to  those  of  the  Marquette  district.     They 

oMon.  U.  S.  Geol.  Survey,  vol.  28,  1897. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE. 


93 


are,  however,  rarely  intruded  by  greenstone  eruptives,  and  are  mtiSi'mbre 
crumpled  than  are  the  Marquette  rocks. 

In  the  same  region  are  two  belt.s  of  oreenstone-scliists  closelj'  analogous  in 
general  appearance  with  those  of  the  Marquette  region.  The  southern  oub  of  these 
borders  for  a  long  distance  the  southern  granite  area,  separating  the  granite  from 
the  detrital  roclts  farther  north.  The  inclination  of  the  greenstone-schists  is  ahiiost 
vertical,  there  being  generally  a  slight  southern  departure  from  verticality.  Very 
high  southern  dips,  often  approaching  verticality,  also  prevail  among  the  layers  of 
the  detrital  succession  itself,  although  here  frequently  occur  reverse  dips  to  the 
northward,  often  at  a  flatter  angle  [p.  25]. 

With  respect  to  the  age  of  the  greenstone-schists,  Irving  writes : 

In  mj'  own  studies  in  the  Menominee  region,  made  in  the  summers  of  1883  and 
1885,  I  became  early  impressed  with  the  close  similarity  between  the  greenstone- 
schists  of  the  Menominee  River  and  those  which  underlie  the  ii'on-bearing  series  of 
Marquette;  with  the  entire  similarity  between  the  rest  of  the  stratiform  rocks  of 


Fig.  12.— Hypothetical  section  across  the  Menoniinee  region  in  the  vicinity  of  Quinnesec  Valley.  After  R.  D.  Trying,  1890; 
A,  basiil  sericitic  quartz-slates;  B,  quartzite;  C,  limestone;  D,  iron  horizon;  E,  slates  and  quartzites;  G,  granite;  Sch, 
schists  of  the  Laurentian.    Scale,  13,000  feet  to  the  inch. 


the  region  and  those  of  the  Marquette  district;  with  the  essential  identity  in  character 
of  the  granite  areas  lying,  respectively,  on  the  northern  and  .southern  sides  of  the 
Menominee  River;  with  the  granitic  intrusions  met  with  in  the  greenstone-schists 
bordering  the  .southern  granite,  and  with  the  striking  conti'a.st  between  the  nature 
of  this  contact  and  that  of  the  northern  granite  and  the  detrital  rocks  which  border 
it  to  the  south.  In  the  latter  case,  the  granite,  instead  of  sending  intrusions  into  the 
rocks  which  rest  against  it,  has  furnished  fragments  to  them,  as  may  be  mo.st  beauti- 
fully seen  at  the  Falls  of  Sturgeon,  Sturgeon  River,  on  the  eastern  side  of  sec.  8,  T. 
39,  R.  28  W.,  Micliigan.  These  considerations  naturally  led  me  to  the  conclusion 
that  the  whole  structure  in  this  district  is  similar  to  that  already  described  as 
obtaining  in  the  Marquette  region,  namely,  that  the  granitic  masses  had  intruded 
themselves  in  the  shape  of  great  bosses  into  rocks  now  represented  by  the  greenstone- 
schists,  after  which  followed  a  protracted  period  of  disturbance  and  denudation 
before  the  deposition  of  the  overlying  detrital  and  iron-bearing  rocks  of  the  region. 
Taking  Major  Brooks's  detailed  map  of  the  Menominee  district,  published  in  the 
atlas  of  the  Wisconsin  survey,  I  platted  on  it  all  of  the  exposures  described   by 


94  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Rominger  and  not  mapped  by  Brooks,  which  exposures  amount  in  all  to  a  large 
number.  Examining,  then,  the  more  important  of  the  exposures  of  the  region,  I 
encountered  still  others,  which  were  also  platted  upon  the  same  map.  Two  sections 
were  then  constructed  across  the  district  from  southwest  to  northeast,  upon  which 
were  platted  all  of  these  exposures,  with  their  dips;  and  it  should  be  said  that  very 
many  new  facts  in  this  direction  have  been  developed  of  late  j'ears  by  mining 

It  has  thus  become  evident  that  a  structure  such  as  is  indicated  in  the  accompa- 
nying fig.  3  [reproduced  as  fig.  12,  p.  93]  would  not  only  coincide  with  the  recorded 
facts  as  well  as  the  sections  of  Brooks  *  *  *  but  very  much  better  than  those 
[pp.  29-80]. 

With  reference  to  the  conglomerates  at  the  Falls  of  the  Sturgeon,  the 
author  says  that  the  granitic  fragments  occur  in  a  fine-grained,  slaty  rock, 
in  which  there  is  a  great  deal  of  sericitic  material,  which  at  times  gives  the 
slate  somewhat  the  look  of  a  crystalline  schist.  This  fact,  together  with 
the  slight  inclination  from  the  vertical  toward  the  north,  led  Credner  to 
include  the  conglomerates  with  the  Laurentian  granite.  Brooks's  view  is 
regarded  as  the  correct  one — i.  e.,  the  conglomerate  is  at  the  base  of  the 
sedimentary  series.  The  granite  sheet  described  by  Rominger  as  inter- 
leaved with  the  conglomerates  could  not  be  found.  Irving  also  points  out 
the  fact  of  Rominger's  inconsistency  in  making  the  same  granite  yield 
fragments  to  the  sedimentaries  and  subsequently  to  intrude ,  them.  The 
nature  of  the  pebbles  and  the  structure  of  the  matrix  which  holds  them  are 
clear  evidence  to  Irving  that  "we  have  here  to  do  with  a  detritus  derived 
by  water  action  from  the  granitic  and  gneissic  area  immediately  to  the 
north.  The  slight  inclination  from  the  vertical  toward  the  granite  which 
these  conglomeratic  schists  sometimes  show  is,  of  course,  no  argument 
against  their  having  been  deposited  upon  the  granite  as  a  substratum." 
(Footnote,  p.  30.)  The  map  accompanying  the  paper  shows  the  distribution 
of  the  Archean,  Algonkian,  and  Cambrian  areas  within  the  district. 
Although  largely  a  compilation,  it  outlines  definitely  for  the  first  time  the 
limits  of  the  iron-bearing  series.     A  reproduction  of  it  forms  PI.  V. 

Williams,  G.  H.  The  greenstone  schist  areas  of  the  Menominee  and  Marquette 
districts,  Michigan:  Bull.  U.  S.  Geol.  Survey  No.  62,  pp.  31-131  and  192-217. 
1890. 

Dr.  Williams's  work  is  purely  microscopical.  The  aim  of  his  paper  is 
"to  trace  each  of  the  rock  types  represented  within  the  areas  studied  from 
its  least  altered  to  its  most  altered  form,  and  to  discover  what  ma}'  have 


U.  S.GEOLOOICAL   SURVEY 


MONOGRAPH  XLVI   PL.V 


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OUTLINE  GEOLOGIC  MAP  OF  THE  MENOMINEE  IRON  REGION 

Compiled  byR.D.Irving  from  maps  byT.B. Brooks,  C.E.Wright, and  C . Rominger, and  from  original  observations 


Scale  of  miles 


1890 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  95 

been  the  agencies  which  produced  the  changes  noticed."  The  object  of  the 
author's  investigations  "was  to  discover,  if  possible,  the  origin  of  the 
greenstone-schists  of  the  Lake  Superior  region,  and  at  the  same  time  to 
afford  a  contribution  to  our  knowledge  of  the  metamorphism  of  basic 
eruptive  rocks  in  general"  (p.  31). 

The  areas  in  the  Menominee  district  selected  for  special  study  are  five 
in  number,  embracing  the  vicinity  of  the  Sturgeon  Falls  and  the  areas  around 
the  Little  and  the  Big  Quinnesec  Falls,  the  Fourfoot  Falls,  and  the  Twin 
Falls.  At  the  Sturgeon  Falls  the  rocks  on  the  Michigan  side  of  the  river 
consist  of  five  bands  of  saussuritized  gabbro  and  four  bands  of  greenstone- 
schists.  The  gabbro  constitutes  Brooks's  bed  XV.  In  thin  section  it  shows 
a  gradation  from  an  almost  massive  pyroxene-bearing  saussuritized  gabbro 
to  schistose  varieties  composed  of  saussurite,  quartz,  and  hornblende.  The 
green  schists  associated  with  this  gabbro  are  plainly  the  result  of  dynamic 
agencies.  In  some  of  them  broken  feldspar  crystals  may  be  detected,  but 
others  are  now  composed  exclusively  of  chlorite,  quai'tz,  and  calcite.  These 
schists  are  believed  to  be  derived  from  the  gabbro  by  pressure  and  shearing. 
Associated  with  them  are  several  bands  of  light-colored  sericite-schists 
which  the  author  considers  as  having  been  produced  from  the  same  gabbro 
by  chemical  processes  that  are  essentially  different  from  those  that  gave 
rise  to  the  green  schists. 

At  the  Little  Quinnesec  Falls  the  rocks  are  mainly  diorites,  diabases, 
chlorite-schists,  and  sericite-schists.  The  great  gabbro  ridge  of  Major 
Brooks,  described  as  extending  along  the  Michigan  side  of  the  river,  is  in 
composition  a  diorite,  originally  containing  a  brown  hornblende  that  has 
been  rej^laced  by  a  green  variety  of  the  same  mineral.  It  is  possible, 
according  to  the-  author,  that  the  brown  hornblende  may  in  turn  have  been 
derived  from  diallage  and  the  rock  may  have  been  a  diabase.  By  further 
alteration  the  green  hornblende  passes  into  a  tremolitic  mineral  and  into  a 
colorless  chlorite.  The  schists  are  believed  to  be  pressure-changed 
diabases.  The  slaty  rocks  recorded  by  Brooks  as  occin-ring  here  are 
thought  to  be  altered  basic  eruptives,  since  they  grade  into  massive  diabases, 
and  under  the  microscope  their  thin  sections  show  evidence  of  the  close 
relationship  existing  between  them  and  the  massive  beds.  The  author 
gives  a  clear  statement  of  the  evidence  from  which  he  concludes  that  the 
massive  rocks  pass  into   schists   by  pressure    action.     He    illustrates    his 


96  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

remarks  by  the  picture  of  a  hand  specimen  taken  from  the  western  end  of 
the  "diorite  ridge"  near  the  falls.  It  shows  a  rock  traversed  by  cross 
gashes,  which  the  author  explains  as  due  to  the  stretching  of  the  rock  after 
solidification. 

At  the  Big  Quinnesec  Falls  the  rocks  below  the  falls  are  dark, 
more  or  less  schistose  greenstones  that  were  once  diabases.  At  the  falls 
and  for  a  half  a  mile  above  them  are  exposed  light-colored  granular 
greenstones  which  graduate  into  sericite-schists.  At  the  Horserace  Rapids 
the  rocks  forming  the  steep  walls  of  the  gorge  are  coarse-grained  diorites. 
These  rocks  and  those  at  the  falls  are  cut  by  bands  of  granite,  gneiss,  and 
schistose  porphyries  that  are  closely  related  genetically  with  the  granite 
south  of  the  Menominee  (Brooks's  Huronian  granite  bed  XX).  The  rocks 
below  the  falls  show  the  effects  of  pressure  in  a  striking  degree.  They 
were  once  diabasic,  but  at  present  they  show  only  obscure  traces  of  their 
ophitic  structure.  The  barrier  rock  of  the  falls  was  regarded  by  Credner 
as  very  similar  to  a  gabbro.  Williams,  however,  finds  it  to  be  essentially 
a  dioi'ite,  although  originally  it  may  have  been  a  hornblende-gabbro,  or 
possibly  a  normal  gabbro.  The  coarse-grained  diorites  of  the  "Horserace" 
(above  the  falls)  are  dioritic  varieties  containing  talc,  which  has  been 
derived  from  hornblende.  The  I'ocks  appear  to  be  much-squeezed 
diabases.  The  green  schists  are  cut  by  dikes  of  granites  and  of  quartz- 
porphyries  that  are  usually  foliated  like  the  schists  themselves.  Usually 
their  foliation  is  pai'allel  to  the  foliation  of  the  surrounding-  rocks  without 
respect  to  the  direction  in  which  the  dikes  run;  thus  it  may  sometimes  be 
parallel  to  the  sides  of  the  dikes  and  at  other  times  may  be  inclined  to 
them.  Most  of  the  acid  bands  are  regarded  as  apophyses  of  the  gi-anite  to 
the  south.  If  they  are  offshoots  of  the  granite,  this  rock  is  younger  than 
the  schists;  and  if  the  schists  are  the  uppermost  members  of  the  Huronian 
series,  the  granite  must  be  the  youngest  rock  in  this  series.  The  writer 
does  not  attempt  to  decide  as  to  the  age  of  the  green  schists,  however,  and 
conseqviently  he  makes  no  supposition  as  to  the  age  of  the  granite  with 
respect  to  the  sedimentary  beds  of  the  Huronian. 

With  reference  to  the  acid  dikes,  the  author  writes: 

The  dikes  when  small  are  iiue  grained  and  felsitic,  but  when  larger  their 
textui'e  is  coarser,  and  they  have  frequently  a  well-developed  schistose  structure 
parallel  to  that  of  the  adjoining  schists.  After  a  careful  examination  of  this  locality 
and  of  the  exposures  between  it  and  the  river,  there  is  no  doubt  in  the  writer's 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  97 

iniiid  that  the  g-ranite,  "  Augen-gneiss,"  biotitic  gneiss,  and  schistose  porphyry 
(or  "porphyroid,"  as  Credner  called  this  rock)  visible  near  the  Upper  [Big]  Quin- 
nesec  Falls  and  along  the  Horserace  are  also  dikes  or  apophyses  connected  with 
the  main  southern  granite  area.  The  schistose  or  banded  structure  of  these  rocks, 
where  such  exists,  is  a  secondary  feature,  produced  by  the  same  dynamic  agencies 
which  rendered  the  greenstones  themselves  schistose  [p.  111]. 

The  granite  of  the  main  southern  granite  area  is  a  typical  granite  with 
a  tendency  to  a  porphyritic  structure.  Like  all  the  rocks  in  the  vicinity  it 
bears  the  marks  of  having  been  crushed. 

At  the  Fourfoot  Falls  the  greenstones  are  again  Avell  exposed.  On 
the  Wisconsin  side  of  the  river  they  are  schistose  and  on  the  Michigan  side 
on  the  strike  of  these  schists  the  rocks  are  massive.  A  quarter  of  a  mile 
below  the  Chicago  and  Northwestern  Railway  bridge  is  an  exposure  of 
black  slate  with  the  typical  structure  of  a  sedimentary  rock.  Above  the 
railroad  bridge  a  few  steps  begin  the  greenstone-schists,  which  are  entirel}^ 
different  from  the  slate,  but  are  similar  to  the  green  schists  already  described. 
At  the  Twin  Falls  the  greenstones  are  of  a  dark,  aphanitic  variety,  and 
when  schistose,  resemble  a  chloritic  slate.  Transitions  between  massive 
diabases  and  greenstone-schists  and  between  these  latter  rocks  and  chlorite- 
sehists  are  traced  by  the  author  step  bj^  step,  so  that  there  can  seem  to  be 
no  question  but  that  the  schists  are  squeezed  eruptive  rocks. 

In  summarizing  the  evidence  as  to  the  origin  of  the  green  schists 
derived  from  their  study  in  the  field  and  laboratory,  the  author  shows  that 
the  foliation  of  the  schists  is  no  proof  of  their  sedimentary  character.  The 
foliation  of  these  rocks  is  parallel  to  the  foliation  of  the  sedimentary  beds 
of  the  iron-bearing  formation,  but  not  always  to  the  strike  of  their  beddino-. 
Both  the  schistosity  of  the  greenstones  and  of  their  associated  granites  is  a 
phenomenon  due  to  pressure,  which  probably  acted  in  two  different  jjeriods, 
in  one  of  which  the  genuine  sediments  received  also  their  foliation. 

The  most  convincing  proof  that  the  rocks  of  the  Menominee  and  Marquette 
greenstone  areas  are  of  igneous  origin  is  not  to  be  derived,  however,  from  their  field 
relations,  but  rather  from  theii-  microscopical  structure.  It  is  true  that  there  are 
many  cases  where  rocks  of  widely  dissimilar  origin  resemble  one  another  so  closelj^ 
that  not  even  the  minutest  study  of  their  internal  structure  is  able  to  distinguish  them 
with  certainty;  nevertheless  there  are  in  other  cases  well-marked  peculiarities  of 
structure  which  may  be  regarded  as  unfailing  indications  that  the  rock  possessing 
them  has  crystallized  out  of  a  molten  magma  [p.  195]. 

MON  XLVI — 04 7 


98  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  structures  that  are  characteristic  of  eruptive  rocks  and  that  have 
been  recognized  in  the  Menominee  greenstones  are  the  ophitic,  the  porphy- 
ritic,  the  micropegmatitic  and  granophyric,  and  the  poikiUtic.  The  original 
rocks  still  recognizable  in  the  Menominee  district  and  those  from  which  the 
schists  have  been  derived  are  gabbros,  diabases,  diabase-porphyries,  diorites, 
and  diorite-porphyries  among  the  basic  phases,  and  granites,  granite- 
porphyries,  and  quartz-porphyries  among  the  acid  areas.  The  evidence  of 
the  microscope  indicates  that  the  greenstones  solidified  at  the  surface. 

In  the  Menominee  Valley  this  evidence  consists  (1)  of  the  tine  texture  of  the 
rocks,  and  (2)  of  the  alternation  of  bands  of  different  types,  which  probably  in  their 
original  position  represented  successive  flows.  Fineness  of  grain  is  universal  in  the 
Menominee  greenstones,  and  we  may  be  certain  that  it  was  a  primary  feature  in  spite 
of  the  extensive  alteration  of  these  rocks.  It  is  especially  noticeable  in  the  case  of 
the  gabbro,  which  is  almost  always  a  coarse-grained  rock  when  it  has  solidified  at 
any  depth.  The  succession  of  massive  beds,  like  the  pale  gabbros  and  the  dark 
diabases  seen  at  the  Lower  [Little]  Quinnesec  Falls,  are  difficult  to  account  for  except 
by  supposing  that  they  were  once  horizontal  sheets  that  flowed  over  one  another 
and  which  were  subsequently  elevated  into  their  present  nearly  vertical  ])osition. 
Traces  of  tuff'  material  are  not  as  distinct  here  as  in  the  Marquette  region,  although 
indications  of  its  existence  are  b3^  no  means  wanting.  We  might  reasonably  expect 
that  any  original  scoriaceous  or  amygdaloidal  structure  would  have  disappeared  in 
the  course  of  the  profound  chemical  changes  through  which  these  greenstones  have 
passed  [pp.  200-201]. 

The  author's  jjaper  is  illustrated  by  maps  of  the  districts  studied  and 
by  12  lithographic  reproductions  of  thin  sections  of  chai-acteristic  rocks. 

1891. 

Van  Hise,  C.  R.  An  attempt  to  harmonize  some  apparently  conflicting  views 
of  Lake  Superior  stratigraphy:  Am.  Jour.  Sci.,  3d  series,  vol.  41,  pp.  117-136.     1891. 

The  author  believes  that  many  of  the  difficulties  that  have  arisen  among 
geologists  vrith  respect  to  the  correlation  of  the  pre-Cambrian  rocks  is  due 
to  the  neglect  to  note  the  existence  of  a  physical  break  in  the  series  of 
strata  placed  by  Irving  in  his  Hurouian  group.  He  shows  that  such  a 
break  occurs  in  the  Marquette  district  and  that  here  there  is  a  well- 
defined  upper  and  a  distinct  lower  series,  separated  from  each  other  by  a 
great  unconformity  and  a  basal  conglomerate.  In  the  Menominee  district 
the  evidence  of  this  break  is  lacking,  possibly  because  the  knowledge  of 
the  relations  existing  between  the  Menominee  rocks  is  less  exact  than  it  is 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  99 

in  the  case  of  the  Marquette  sediments.  It  is  thoug-ht  probable,  however, 
that  ill  the  Menominee  district  the  equivalents  of  both  the  lower  and  upper 
Marquette  rocks  occur.  The  Menominee  proper — that  is,  the  portion  of  the 
Menominee  district  east  of  the  Menominee  River — is  thought  to  correspond 
in  position  with  the  Lower  Marquette  and  that  portion  west  of  the  river 
with  the  Upper  Marquette. 

GoETZ,  George  W.  Analyses  of  Lake  Superior  ores:  Trans.  Am.  Inst.  Min. 
Eng.,  vol.  19,  pages  59-61.     1891. 

The  author  records  the  results  of  analyses  of  ores  from  24  mines  in  the 
Menominee  district  on  both  sides  of  the  Menominee  River. 

1892. 

Van  Hise,  C.  R.  Correlation  papers — Archean  and  Algonkian:  Bull.  U.  S. 
Geo!.  Survey  No.  86,  pp.  72-208,  470-529.  With  general  map  of  Lake  Superior 
region.     1892. 

This  volume  contains  a  summary  of  all  the  work  done  on  the  pre- 
Cambrian  rocks  of  North  America  up  to  within  a  few  months  of  the  time 
the  volume  was  pubhshed.  The  evidence  collated  from  the  writings  of 
those  geologists  who  had  investigated  Lake  Superior  geology  is  discussed 
and  conclusions  are  drawn  from  it  by  the  author.  With  the  abstract  of  the 
literature  we  have  nothing  to  do  in  this  review,  nor  with  the  matter  dealing 
with  the  classification  of  the  pre-Cambrian  formations  in  the  Lake  Superior 
region.  The  latter  subject  is  freely  discussed  in  tlie  chapter  on  literature 
in  the  Marquette  monograph,"  where  the  discussion  rightly  belongs,  since 
many  of  the  conclusions  arrived  at  with  reference  to  the  separation  of  the 
pre-Cambrian  series  were  reached  very  largely  by  studies  prosecuted  in 
the  Marquette  district.  There  are,  however,  a  few  direct  references  made 
to  the  Menominee  district  which  should  be  considered  liere. 

Li  1890  the  author  examined  the  rock  succession  at  Iron  Mountain, 
finding  above  the  ore  formation  at  the  Ludington  and  Chapiii  mines  a  con- 
glomerate which  bears  fragments  of  ore  and  jasper.  "It  therefore  appears 
that  after  this  material  reached  its  present  condition  in  the  ore-bearing  series 
it  was  eroded  and  furnished  debris  for  a  newer  series"  (p.  156).  In  com- 
pany with  Professor  Pumpelly  he  again  in  1891  and  1892  examined  the  ore 
formation.     In  a  quarry  east  of  the  Chapin  mine,  and  also  in  the  deeper 

"Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897,  pp.  .5-148. 


100  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

workings  of  this  mine,  it  was  discovered  that  the  ores  resting  almost  directly 
upon  the  limestone  bear  a  considerable  percentage  of  carbonates,  and 
in  the  first-mentioned  locality  they  grade  directly  downward  into  the 
limestone. 

It  is  therefore  probable  that  the  ore  formation  of  these  districts,  in  part  at  least, 
is  but  an  upward  continuation  of  the  limestone  formation,  perhaps  differing  from  it 
originally  only  in  that  the  upper  part  contained  a  greater  quantitj^  of  original 
carbonate  of  iron. 

Above  the  ore  formation  at  Quinnesec,  test  pits  show  the  presence  of  a  typical 
chert  and  jasper  conglomerate,  in  every  respect  like  the  basement  conglomerates  of 
the  Upper  Marquette  [p.  156]. 

The  additional  evidence  with  respect  to  the  physical  break  in  the 
clastic  series  lying  between  the  green  schists  and  the  Potsdam  sandstone  is 
summarized  as  follows: 

In  the  Menominee  district  as  evidence  in  favor  of  a  physical  break  within  the 
clastic  series  are  the  conglomerates  described  by  Brooks  at  the  Pine  and  Poplar 
rivers  district,  and  in  the  Commonwealth  section.  *  *  *  Also,  the  structui-al 
break  indicated  by  these  conglomerates  is  supported  by  Brooks's  major  divisions  of 
the  Menominee  rocks.  His  inferior  Huronian  comprises  the  lower  quartzite  of  great 
thickness,  a  great  marble  formation,  and  the  great  iron-ore  horizon,  consisting  of 
magnetitic,  hematitic,  and  jaspery  schists,  with  deposits  of  iron  ore.  In  this 
formation  are  the  Norway,  Quinnesec,  Ludington,  Chapin  mines,  etc.  Brooks's 
middle  Huronian,  presumably  above  the  unconformity,  includes  quartzites,  clay 
slates  and  obscure  soft  schists.  Within  these  soft  slates  is  the  upper  iron-beai'ing 
horizon,  including  such  mines  as  the  Commonwealth,  those  at  Crystal  Falls,  etc. 
[Pp.  180-181.] 

The  author  does  not  believe  that  a  correspondence  can  be  made  out 
between  the  subordinate  members  of  the  Menominee  and  Marquette 
districts,  and  yet  he  thinks  that '  the  Menominee  district  in  Michigan 
corresponds  as  a  whole  to  the  Lower  Marquette  series. 

Van  Hise,  C.  R.  The  iron  ores  of  the  Marquette  district  of  Michigan:  Am. 
Jour.  Sci.,  3d  series,  vol.  43,  pp.  116-132.     1892. 

Although  this  article  deals  mainly  with  the  manner  of  occurrence  of 
the  ore  bodies  in  the  Marquette  district,  those  of  the  Menominee  district  are 
referred  to  in  a  few  words.  The  ores  of  this  district  are  said  to  occur  in 
Iwo  formations,  one  of  which  belongs  with  the  Lower  Menominee  and  the 
'Other  with  the  Upper  Menominee.  From  the  general  work  done  in  the 
<district  it    seems    that    the    ores    are    all    secondary    concentrations  upon 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  101 

impervious  formations.  They  are  particularly  likely  to  be  of  large  size 
when  the  impervious  beds  are  folded  or  when  two  of  them  combine  to 
form  pitching  troughs. 

WiNCHELL,  N.  H.  The  crystalline  rocks — some  preliminary  considerations  as 
to  their  structure  and  origin:  Twentieth  Ann.  Rept.  Minnesota  Geol.  and  Nat. 
Hist.  Survey  for  1891,  pp.  1-28.      1893. 

The  first  part  of  this  article  is  a  general  discussion  of  the  nature  of  the 
evidence  that  should  guide  the  geologist  in  his  conclusions  as  to  the  origin 
of  the  metamorphic  rocks.  The  second  part  illustrates  the  author's  use  of 
this  evidence.  He  declares  that  field  evidence  is  of  more  value  in  deter- 
mining the  sedimentary  origin  of  a  banded  rock  than  the  evidence  of  a 
microscope.  He  illustrates  by  reference  to  the  greenstone-schists  of  the 
Menominee  district.  He  reproduces  the  figure  of  the  hand  specimen  with 
cross  gashes  published  by  Williams,  and  seems  to  conclude  that  the  rock 
which  Williams  declared  to  be  a  squeezed  gabbro  is  a  squeezed  sedimentary 
rock.  The  greenstones,  it  seems  from  a  careful  reading  of  the  author's 
words,  are  thought  to  be  sedimentary  deposits,  in  large  part  tuffaceous. 

Wadsworth,  M.  E.  Sketch  of  the  geology  of  the  iron,  gold,  and  cojaper  dis- 
tricts of  Michigan  (dated  March  26th,  1892):  Report  of  State  Board  of  Geol.  Survey 
for  the  years  1891  and  1892,  pp.  75-174.     1893. 

The  Azoic  or  Archean  rocks  of  Michigan,  according  to  the  author, 
embrace  three  distinct  formations,  named,  from  their  typical  exposures  in 
the  Marquette  district,  the  Cascade,  the  Republic,  and  the  Holyoke.  The 
Cascade  is  the  oldest.  In  the  Menominee  district  it  contains  gneisses  in 
which  are  embedded  gneissoid  fragments,  and'  true  granites  which  hold  an 
intrusive  relation  to  the  gneisses  and  other  foliated  rocks.  In  sec.  2,  T.  40  N., 
R.  30  W.,  a  basic  dike,  now  an  amphibole-schist,  was  seen  to  be  intrusive 
in  quartzite,  and  in  its  turn  to  be  cut  by  a  felsite  dike.  The  Republic  for- 
mation corresponds  to  Van  Hise's  Lower  Huronian. 

The  heavy  quartzite  which  extends  in  the  Menominee  district  from  Sturgeon 
River  along  Pine  River  *  *  *  i,.;  thought  to  belong  to  the  base  of  the  Republic 
formation,  as  it  is  found  in  various  places  close  to  the  Cascade  gneiss  and  granite,  dip- 
ping away  from  that  formation,  and  is  cut  by  dikes  of  the  granite  on  sec.  12,  T.  -tl, 
R.  30  W.  This  quartzite  is  probably  Republic,  if  the  overlying  ores  are  Republic, 
which  they  are  here  considered  to  be,  although  no  direct  proof  of  this  supposition  has 
yet  been  obtained.  The  ground  for  this  belief  rests  chiefly  on  the  physical  character 
of  the  ore  formation  [p.  103]. 


102  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

In  addition  to  the  quartzite  and  iron  ores  the  dolomites  so  abundantly- 
exposed  in  the  Menominee  district  are  also  jjlaced  in  the  Republic  formation. 
The  author  calls  attention  to  the  existence  of  "eruptive  argillite  or  schist" 
in  dikes  at  the  Cyclops  and  Norway  mines.  In  connection  with  the  discus- 
sion of  the  origin  of  the  greenstone-schists,  Wadsworth  states  that  the  rock 
on  the  Michigan  side  of  the  Menominee  River,  below  the  Little  Quinnesec 
Falls,  and  at  the  Big  Quinnesec,  is  a  conglomeratic  greenstone  or  a  tuff, 
and  not  an  eruptive  diabase  or  diorite,  as  Williams  supposed.  Similar  tuffs 
are  very  common  in  the  Marquette  district. 

HuBBABD,  L.  L.  Macroscopic  minerals  of  Michigan:  Report  of  State  Board  of 
Geol.  Survey  for  the  year  1891  and  1892,  pp.  174-176.     1893. 

In  this  list  of  minerals  occurring  in  Michigan  the  author  mentions 
chalcopyrite,  pyrite,  quartz,  hematite,  limonite,  martite,  laumontite,  malaco- 
lite,  orthoclase,  staurolite,  tourmaline,  azurite,  calcite,  dolomite,  siderite, 
and  malachite  as  existing  in  the  Menominee  district. 

Patton,  H.  B.  Microscopic  study  of  some  Michigan  rocks.  Report  of  State 
Board  of  Geol.  Survey  for  the  years  1891  and  1892,  pp.  184-186.     1893. 

As  the  result  of  his  investigation  of  thin  sections  of  Marquette  and 
Menominee  rocks  Patton  identifies  a  great  variety  of  schists  in  these  two 
districts,  besides  slates,  graywackes,  and  several  kinds  of  eruptive  rocks, 
but  he  gives  no  details  with  respect  to  any  occurring  in  the  Menominee 
district. 

WrLLiAMS,  G.  H.  The  microscope  and  the  study  of  the  crystalHne  schists: 
Science,  vol.  21,  p.  1.     1893. 

In  a  reply  to  Professor  Winchell's  article  on  the  crystalline  rocks, 
referred  to  above.  Dr.  Williams  takes  exceptions  to  some  of  Winchell's 
remarks  with  respect  to  the  comparative  value  of  field  and  microscopical 
evidence  in  the  study  of  the  crystalline  schists.  He  calls  attention  to  the 
fact  that  the  figures  reproduced  by  Winchell  from  the  author's  paper  are 
figures  of  S2iecimens  taken  from  rock  masses  that  were  so  clearly  eruptive 
in  origin  that  there  was  no  necessity  for  their  study  under  the  microscope. 
In  conclusion,  he  writes  : 

In  reaUty.  what  are  known  in  the  Lake  Superior  region  as  "greenstones"  and 
"greenstone-schists"  are  not  one  thing,  but  a  great  variety  of  different  things.  Some 
of  them  are  massive  lavas,  others  accumulations  of  ash  material,  stratified  by  gravity 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  103 

or  water.     Thej'  possess  structures  of  diverse  origin,  which  may  to  the  field  geologist 
appear  very  much  alike. 

BiRKiNBiNE,  John.  Iron  ores:  Mineral  Resources  U.  S.  for  1891,  pp.  lU-46. 
1893. 

The  author,  besides  giving  the  usual  statistics  concerning  the  iron-ore 
industry  in  the  United  States,  abstracts  from  Commissioner  Lawton's  reports 
on  the  Michigan  iron  mines  several  statements  relating  to  the  distribution 
of  the  ore-bearing-  beds  in  the  Menominee  district,  but  no  information  is 
given  concerning  the  iron-bearing  series  in  addition  to  that  given  in  the 
reports  of  Brooks,  Wright,  and  Rominger. 

Van  Hise,  C.  R.  An  historical  sketch  of  the  Lake  Superior  region  to  Cambrian 
time:  Jour.  Geol.,  vol.  1,  pp.  113-128,  with  general  geological  map  of  the  Lake 
Superior  region.     1893. 

In  this  general  sketch  of  the  geology  of  the  Lake  Siiperior  region  the 
Lower  Menominee  rocks  are  made  equivalent  to  the  Lower  Marquette  and 
to  the  Lower  Huronian  in  otlier  portions  of  the  region.  The  map  is  the 
same  as  that  published  in  the  Correlation  Paper. 

Van  Hise,  C.  R.  Sketch  of  the  pre-Cambrian  geology  of  the  Lake  Superior 
region,  with  references  to  illustrative  localities:  Compte-Rendu,  Fifth  Sess.  Inter. 
Geol.  Cong.,  pp.  489-512,  with  maps.     1893. 

In  this  paper  the  author  gives  a  synopsis  of  the  knowledge  concerning 
the  pre-Cambrian  geology  of  the  Lake  Superior  region.  The  facts  recorded 
in  it  are  not  very  diiferent  from  those  mentioned  in  the  Archean-Algonkiau 
Correlation  Bulletin  and  in  other  papers  by  the  same  writer.  With  respect 
to  the  Archean  of  the  Menominee  district,  of  which  Irving's  map  is  repro- 
duced, the  author  makes  the  following  statement: 

In  the  Menominee  district  the  schists  and  granites  of  the  Basement  Complex  may 
be  seen  in  typical  exposures  both  south  and  north  of  the  Huronian  rocks.  The 
northern  schist  area  is  well  exposed  at  Twin  and  Fourfoot  Falls,  3-5  miles  north- 
west of  Iron  Mountain,  while  the  northern  gi-anite  appears  some  miles  northeast  of 
Iron  Mountain.  The  southern  schists  are  finely  exposed  southeast  of  Iron  Mountain 
at  the  Upper  [Big]  Quinnesec  Falls,  at  the  Lower  [Little]  Quinnesec  Falls,  at  Stur- 
geon Falls,  and  near  the  crossing  of  the  Menominee  by  the  Milwaukee  and  Northern 
Railway.  At  the  Hor.serace,  above  Upper  Quinnesec  Falls  and  one-half  mile  to 
the  south,  before  the  solid  granite  is  reached,  numerous  dikes  of  this  rock  may  be 
seen  cutting  the  schists.  On  the  Milwaukee  and  Northern  Railway  the  granite 
rocks  appear  about  •!  miles  south  of  Iron  Mountain.     At  this  point  and  east  and 


104  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

west  of  the  railroad  the  intrusive  relations  between  the  granitic  and  schistose  rocks 
are  finely  shown  [p.  494]. 

The  Lower  Huronian  consists  of  (1)  conglomerates,  quartzites,  quartz- 
schists,  and  mica-schists;  (2)  limestones;  (3)  various  ferruginous  schists; 
and  (4)  basic  and  acid  eruptives,  which  occur  both  as  deep-seated  and  as 
volcanic  rocks.     The  Lower  Menominee  belongs  here. 

It  may  be  best  studied  at  Iron  Mountain  and  vicinity  and  at  Norway  and  vicinity. 

At  these  places  the  iron-bearing  member  and  the  limestone  are  well  exposed  [p.  496]. 
In  the  Menominee  district  the  only  locality  at  which  the  supposed  Lower  Huron- 
ian is  known  to  be  in  direct  contact  with  the  Basement  Complex  is  at  the  falls  of 
Sturgeon  River.  Here  the  Basement  Complex  has  its  typical  character.  It  consists 
of  coarse,  black,  hornblendic  gneiss,  which  is  cut  through  and  through  by  red  granite. 
Both  occur  in  large  masses,  and  along  the  numerous  contacts  the  granite  and  gneiss 
are  often  minutely  interlaminated,  evidently  by  the  intrusion  of  the  latter.  At  many 
places  dikes  of  granite  may  be  seen  passing  from  large  granite  masses  and  penetrat- 
ing the  schists,  and  then  gradually  dying  out.  In  places  the  schists  are  so  cut  by 
stringers  of  granite  as  to  have  a  genuine  pegmatized  appearance.  Upon  the  irregu- 
lar eroded  surface  of  this  Basement  Complex  rest  masses  of  the  broken  ledge  2  or  3 
feet  thick,  which  pass  upward  into  a  schistose  conglomerate  conta:ining  numerous 
well-rounded  bowlders  and  pebbles  of  the  granite-gneissoid  schist,  in  every  respect 
like  these  rocks  in  the  Complex  below.  The  matrix  of  the  schist  is  sheared  and 
crystalline,  but  the  larger  pebbles  and  bowlders  of  granite  have  escaped  any  consid- 
erable crushing.  There  are  several  alternations  of  coarse  conglomerate  and  line  sili- 
ceous schist  before  the  conglomerate  finally  grades  into  the  overlying  quartzite. 
The  geology  has  not  been  worked  out  in  detail  here,  and  that  this  formation  is  the 
lower  quartzite  of  the  Lower  Huronian  rests  upon  the  authority'  of  Brooks  [pp. 
499-500]. 

The  Upper  Huronian  is  not  as  well  exposed  on  the  Michigan  side  of 
the  Menominee  River  as  it  is  on  the  Wisconsin  side.  "The  lowest  forma- 
tion of  the  Upper  Huronian  may  be  seen  above  the  Lower  Huronian  iron 
formation  at  Iron  Mountain  and  Quinnesec.  The  series  can,  however,  best 
be  studied  about  the  Commonwealth  mine  and  2  or  3  miles  to  the  west- 
ward in  the  vicinity  of  Lake  Eliza"  (p.  503).  The  Upper  and  the  Lower 
Huronian  are  often  separated  by  unconformities  and  basal  conglomerates. 
"In  the  Menominee  district  the  basal  conglomerate  of  the  Upper  Huronian 
is  not  well  exposed,  but  has  been  detected  at  the  Chapin  and  Quinnesec 
mines  by  shafts  and  drill  holes"  (p.  506). 

HuLST,  N.  P.  The  geology  of  that  portion  of  the  Menominee  Range  east  of  the 
Menominee  River:  Proc.  Lake  Superior  Min.  Inst,  for  March,  1893,  pp.  19-29, 
with  map.     1893. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  105 

The  author  gives  an  abstract  of  the  general  geology  of  the  Menominee 
district  as  worked  out  by  Brooks  and  adds  detailed  sections  of  several  of 
the  mines  in  that  portion  of  the  district  east  of  the  Menominee  River.  The 
ore  bodies  are  described  as  being  found  in  beds  of  banded  lean  jasper, 
which  is  always  associated  with  the  richer  ore.  The  ore  may  occur  any- 
where within  the  jaspery  horizon.  It  is  crossed  by  the  stratification  planes, 
which  are  extensions  of  those  in  the  jasper.  Often  there  are  spots  in  the 
jasper  composed  of  a  substance  that  appears  to  be  in  a  transition  state 
between  jasper  and  ore.  The  silica  seems  to  be  gradually  disappearing 
from  the  jasper  by  solution,  leaving  a  mass  continually  growing  richer  in 
the  ore  material. 

The  ore  bodies  usually  pitch  west  at  from  30°  to  50°.  Some  of  them 
rest  upon  a  foot  wall  of  soapstone  or  are  under  a  hanging  wall  of  this  sub- 
stance. Others  possess  no  distinct  walls,  the  merchantable  ore  suddenlv 
giving  away  to  the  lean  ore,  or  vice  versa,  according  to  no  rule.  The  pro- 
ductive portions  of  the  range  appear  to  be  located  at  points  where  the  for- 
mations have  been  faulted,  eroded  deeply,  or  sharply  folded. 

The  limestone  is  thought  to  be  beneath  the  ore-bearing  formation  and 
not  above  it.  The  northerly  dip  of  this  rock  at  the  Quinnesec,  Pewabic, 
Chapin,  and  other  mines  in  the  western  portion  of  the  district  is  explained 
as  due  to  an  overturn  of  the  series.  Attention  is  called  to  the  fact  that 
the  discovery  of  bowlders  of  limestone  in  the  iron  formation  by  Wright  is 
corroborative  evidence  in  favor  of  this  view. 

The  descending  succession  at  the  Chapin  and  the  Pewabic  mines, 
obtained  by  cross  sectioning,  is  as  follows: 

Section  at  Chapin  mine. 

Feet. 
Quartzite 

Jasper 

Quartzite 

Quartzite  and  jasper 

Quartzite,  slate,  and  jasper 

Slate  

Quartzite  and  slate 

Quartzite  and  jasper 

Banded  ore,  containing  Millie  ore  body 300 

Quartzite  and  slate | 

Slate J     '^^ 

Jasper 


140 


Ore  body.                                                                                   '  '""^ 
Gray  slate 7,5 


106 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Section  at  Chapin  inine — Continued. 


Ore 

Gray  slate  . 

Jasper 

Gray  slate  . 

Jasper 

Gray  slate  . 

Jasper 

Ore 

Gray  slate  . 
Limestone  . 


Feet. 


185 


Section  at  Pewabic  mine. 


Feet. 
600 


■  about  15 


Quartzite 

Red  slate 

Jasper  and  ore,  containing  Pewabic  ore  body 215 

Gray  slate 112 

Quartz 

Gray  slate 

Quartzite 77 

Quartz  and  slate about  10 

Slate  conglomerate 50 

Red  slate .» 77 

Quartz  and  gray  slate 

Quartzite 

Quartz  and  sand 

Slate  conglomerate 

Quartzite  conglomerate 116 

Red  slate 50 

Jasper .) 


85 


Red,  gray  slate. 
Limestone 


40 


The  normal  dip  of  the  iron-bearing'  series  is  to  the  south.  The 
cause  of  this  southerly  dip  the  author  ascribes  to  the  southern  granite,  the 
Huronian  granite  of  Brooks.  This  is  supposed  to  have  flowed  out  upon 
the  sediments  when  they  were  approximately  horizontal,  and  by  its  weight 
to  have  caused  them  to  sink  beneath  it. 

Although  the  principal  iron-bearing  horizon  is  above  the  limestone,  a 
second  one  is  surmised  to  exist  below  this  bed,  since  the  Loretto  mine  on 
the  Sturgeon  River  has  been  opened  in  rocks  dipping  south,  apparentl}- 
under  the  limestone  north  of  the  main  ore  belt. 

The  map  accompanying  the  article  is  practically  a  reproduction  of  the 
Brooks  map. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  107 

1894. 

WiNCHELL,  H.  V.  Historical  sketch  of  the  discoveiy  of  mineral  deposits  in 
the  Lake  Superior  iron  region:  Second  Ann.  Rept.  Proc.  Lake  Superior  Min.  Inst. 
1(S94.  Also  Twenty-third  Ann.  Rept.  Minnesota  Geol.  and  Nat.  Hist.  Survey  for 
1894,  pp.  116-1.55.     189,5. 

After  quoting  from  Messrs.  Foster  and  Whitney's  description  of  the 
geology  of  the  Menominee  district,  the  author  states  that  in  1866  Messrs. 
Thomas  and  Bartley  Breen  discovered  the  first  workable  deposit  of  ore  on 
the  Menominee  range,  but  not  until  1870  was  any  systematic  work  done  on 
the  deposit.  In  that  year  the  first  openings  were  made  that  afterwards  led 
to  the  development  of  the  Breen  mine.  The  Vulcan  and  the  West  Vulcan 
ore  bodies  were  discovered  by  Dr.  N.  P.  Hulst  in  1872,  the  Quinnesec  in 
1873  by  Mr.  J.  L.  Buell,  and  the  Chapin  in  1878  by  Dr.  Hulst. 

Smyth,  H.  L.  Relations  of  the  Lower  Menominee  and  Lower  Marquette  series 
in  Michigan  (Preliminarv):  Am.  Jour.  Sci.,  3d  series,  vol,.  47,  pp.  216-223.     1894. 

Nearly  all  writers  on  the  geology  of  the  Marquette  and  Menominee 
districts  have  maintained  the  general  equivalency  of  the  iron-bearing  series 
in  the  two  districts.  This  opinion  is  based  on  the  unconformability  of  the 
clastic  series  in  each  district  above  a  series  of  gneisses  and  crystalline 
schists,  and  upon  the  lithological  similarity  that  exists  between  certain 
members  in  both  series. 

The  author's  work  north  of  the  Menominee  River  iron-bearing  area 
confirms  Van  Hise's  view  that  there  is  an  unconformity  in  the  Menominee 
series  corresponding  to  the  unconformity  between  the  Lower  and  the  Upper 
Marquette  rocks.  The  sequence  in  the  two  districts  is  represented  to  be  as 
follows: 

Marquette  district.  Menominee  district. 

Upper  Marquette.  Upper  Menominee. 

Unconformity.  Unconformity. 

Lower  Marquette.  Lower  Menominee. 

Unconformity.  '           Unconformity. 

Arciiean.  Archean. 

Although  the  sequence  appears  to  be  similar  in  both  districts  the 
rocks  of  the  one  region  have  not  been  traced  into  the  other,  so  that  it  can 
not  be  said  that  this  similarity  proves  the  formations  in  the  two  districts 
to  have  been  formed  contemporaneously.  The  likeness  of  the  Lower 
Menominee  to  the  Lower  Marquette  formations  is  rendered  more  striking 


108  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

when  their  lithological  similarities  are  compared  more  carefully  than  has 
heretofore  been  done.  The  Lower  Menominee  (which  is  that  portion  of 
the  Algonkian  most  prominent  in  the  district  under  consideration)  consists  of 
the  following  strata: 

(1)  A  basal  quartzite  from  700  to  1,000  feet  thick. 

(2)  A  crystalline  limestone  from  700  to  1,000  feet  thick. 

(3)  Red,  black,  and  green  slates,  not  known  to  exceed  200  to  300  feet 
in  thickness.  In  these  slates  occur  the  iron  ores  of  Norway  and  Iron 
Mountain. 

(4)  The  highest  member  (except  the  volcanics)  is  a  jasper,  best  devel- 
oped at  Michigamme  Mountain  in  sec.  4,  T.  43  N.,  R.  31  W.,  and  in  sec. 
33,  T.  44  N.,  R.  31  W. 

Iron  ores  occur  at  three  horizons — (1)  in  upper  portion  of  the  quartzite 
near  its  contact  with  the  limestone;  (2)  in  the  slates;  (3)  in  the  Michigamme 
jasper  (not  present  in  the  Menominee  district  as  defined  in  this  monograph). 
Lean  martite  ores  are  widely  distributed  at  the  first  horizon,  but  only  one 
workable  deposit  has  been  found  in  this  position  in  the  series.  The 
important  deposits  are  those  occurring  in  the  slates. 

"These  occur  as  local  concentrations  in  a  ferruginous  rock,  composed 
of  banded  jasper  and  iron  ore,  which,  perhaps,  is  the  modified  representa- 
tive of  portions  of  the  slates  carrying  a  large  proportion  of  nonclastic 
material  of  original  deposition." 

The  lithological  similarity  of  the  Menominee  with  the  Marquette  series 
is  thus  expressed: 

Menominee.  Marquette. 

Michigamme  jasper.  Jasper  banded  with  ore.  1 

»  ■'    •^  ..^         ..        ..     ,.,        ,  .  .Hiron  formation). 

Slate  (principal  iron  formation).  Magnetie-actinolite  schistj^ 

Limestone.  Quartzite. 

Quartzite. 

Archean.  Archean. 

The  correspondence  is  not  as  close  as  it  was  supposed  to  be,  the 
absence  of  limestone  from  the  Marquette  district  being  especially  noticeable. 

The  Michigamme  jasper  was  traced  north  by  its  magnetic  properties 
into  an  area  where  the  rock  exposures  consist  of  a  lower  quartzite  and  an 
upper  magnetite-actinolite  rock.  The  magnetic  line  corresponding  to  these 
beds  was  traced  still  farther  north  until  it  comes  within  2. J  miles  of  a  line 
of  magnetic  attraction  passing  through  the  actinolite-schists  of  the  Marquette 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  109 

series.  The  Menominee  rocks  dip  eastward  while  the  Marquette  rock  is 
thought  to  dip  west.  The  intervening  space  between  the  two  magnetic 
Hues  is  covered  with  drift,  but  presumably  beneath  it  is  a  synclinal  fold, 
with  the  Michigamme  jasper  and  the  Marquette  actinolite-schists  on  the 
corresponding  opposite  sides.  If  this  supposition  is  correct  the  quartzite 
composing  the  lower  portion  of  the  Michigamme  jasper  on  the  Menominee 
side  of  the  syncline  is  the  same  as  the  quartzite  under  the  magnetite-actinolite- 
schists  of  the  Marquette  series,  and  as  a  consequence  the  whole  of  the 
latter  series  is  represented  in  the  Menominee  district  by  the  higher  membei's 
of  the  Menominee  series. 

The    conclusions   of  the    author   as    summarized    by   himself  are  as 
follows : 

1.  The  Lower  Menominee  quartzite,  limestones,  and  slates  are  all  older  than  any 
formation  in  the  Marquette  area. 

2.  The  Michagamme  jasper  was  deposited  in  a  continuous  sheet  over  both 
[Marquette  and  McnoniineeJ  districts,  and  in  the  Marquette  district  con.stitutes  both 
the  iron-bearing  formation  and,  for  most  of  the  area,  the  lower  quartzite. 

3.  The  principal  ore  horizon  of  the  Menominee  has  no  equivalent  in  the  Marquette 
district. 

Van  Hise,  C.  R.,  Summary  of  current  pre-Cambrian  North  American  Litera- 
ture: Jour.  Geol.,  vol.  2,  p.  453.     189-i. 

This  article  consists  of  a  r^sum^  of  Hulst's  article  on  the  Menominee 
district  supplemented  by  the  following  comments: 

.  The  sections  give  additional  evidence  that  in  the  Menominee  district,  as  in  the 
Marquette,  there  are  two  unconformable  series.  The  Chapin,  Ludington,  and 
Hamilton  appear  to  belong  to  the  Lower  Huronian.  The  horizon  of  quartzite, 
slate,  and  conglomerate  is  evidenth'  the  basal  conglomerate  of  the  Upper  Huronian. 
The  Millie,  Pewabic,  and  similar  ore  bodies  are  in  the  Upper  Huronian.  That  the 
ore  bodies  occur  in  disturbed  areas  and  frequently  rest  upon  soapstone  or  other 
impervious  formations  accords  perfectly  with  what  has  been  previously  ascertained 
as  to  the  manner  of  concentration  of  the  Lake  Superior  iron  ores. 

1895. 

RoMiNGER,  C.  Geological  Report  on  the  Upper  Peninsula  of  Michigan,  exhibit- 
ing the  progress  of  work  from  1881-1884;  Iron  and  copper  regions:  Geol.  Survey 
Michigan,  vol.  5,  pp.  1-81.     1895. 

In  this  report  Dr.  Rominger  supplements  his  earlier  report  on  the 
Marquette  and  Menominee  districts  by  recording  his  observations  made 


110  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

between  the  years  1881-1884.  Very  little  additional  information  is  given 
concerning  the  Menominee  rocks,  most  of  the  author's  time  having  been 
spent  in  the  Marquette  and  the  Gogebic  districts. 

The  "granite  seams  intersecting  the  dioritic  rock  series"  south  of  the 
Big  Quinnesec  Falls  and  the  porphyries  of  Pemenee  Falls  are  identified 
as  "analog'ous"  to  the  granites  and  porphyries  cutting  the  green  schists 
north  of  the  city  of  Marquette.  At  Pemenee  Falls  the  porphyries  occur 
not  only  in  dikes,  but  in  "  a  succession  of  porphyritic  beds  of  immense 
thickness"  (p.  7). 

With  respect  to  the  diorite  group  the  author  states  that  the  fine-grained 
dioritic  rocks  near  the  Quiver  Falls  are  all  augitiferous,  as  is  also  the  range 
of  diorites  running  across  the  N.  i  of  T.  40  N.,  R.  30  W.  "llie  liornblende 
in  them  appears  to  be  the  result  of  alteration  of  the  augite."  The  rocks 
of  the  Big  and  of  the  Little  Quinnesec  Falls  are  typical  diorites,  but  the 
baiTier  rock  of  the  Sturgeon  Falls  is  a  gabbro,  as  are  also  the  so-called 
diorites  in  sec.  35,  T.  39  N.,  R.  29  W.,  and  in  the  northwest  quarter  of  sec. 
16,  T.  38  N.,  R.  28  W.  Diallage  was  recognized  in  dikes  of  a  dark-green 
rock,  supposed  to  be  serpentine,  which  cut  the  green  schists  a  short  dis- 
tance above  the  Sturgeon  Falls  and  in  exposures  of  a  similar  rock  in  the 
W.  J  of  sec.  26,  T.  39  N.,  R.  29  W.,  near  the  road  leading  to  Menominee. 
This  rock  and  certain  other  finer-grained  ones  in  the  vicinity  consist  of 
blades  of  diallage  in' a  cement  of  serpentine.  The  rock  in  sec.  12,  T.  39 
N.,  R.  30  W.,  that  in  sec.  9,  T.  37  N.,  R.  28  W.,  on  the  Menominee  River, 
and  at  many  other  places  in  the  district,  also  contains  more  or  less  augite. 

The  ore-bearing  rocks  of  the  Menominee  district  east  of  the  Menom- 
inee River  are  regarded  as  younger  than  the  Felch  Mountain  ore  beds,  as 
young,  perhaps,  even  as  the  older  beds  of  the  author's  mica-schist  group. 
In  the  northwest  quarter  of  sec.  17,  T.  41  N.,  R.  31  W.,  a  little  beyond  the 
limits  of  the  district  studied  in  this  volume,  the  micaceous  schists  have 
been  explored  for  iron.  No  "real  good  ore"  was  found,  but  interlaminated 
with  the  schists  in  their  "lowest  position  right  in  the  surface  of  a  super- 
ficially decomposed  diorite  belt  underlying  these  beds,  and  in  clefts  of  the 
diorite,  pockets  of  a  compact  hydrated  iron  ore  [were  found],  which  to  all 
evidences  has  been  a  secondary  deposit  of  infiltration  a  long  time  after  the 
deposition  of  this  schistose  series  "  (p.  37). 

The  arenaceous   slate  group,   comprising  the    "upper  series   of   the 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  1  1 1 

Huronian  sedimentary  layers,"  contains  even  a  greater  quantity  of  liinon- 
itic  ore  than  had  been  supposed.  "This  younger  group  of  sediments, 
inclosing  limonitic  ore  deposits,  shows  by  its  topographical  distribution  an 
independence  from  the  preceding  lower  strata,  which  proves  considerable 
changes  in  the  ocean  level  during  the  time  intervening  between  the  deposi- 
tion of  the  first  and  the  latter  "  (p.  73). 

In  the  Quinnesec  mining  district  no  interruption  in  the  progress  of 
formation  of  sedimentary  layers  is  indicated,  as  we  find  on  the  north  side 
of  the — 

QuinnesGc  iron  range,  its  latest  strata,  the  great  belt  of  compact  siliceous  lime- 
stones, conformably  succeeded  bj'  this  very  large  group  of  sericite-argillite-schists, 
graphitic  slate-rock  layers,  chert  and  quartzite  belts,  with  interposed  accunmlations 
of  limonitic  iron  ore,  but  farther  northwest,  partly  in  Wisconsin  territorj\  the  most 
common  case  is  to  find  this  upper  series  of  rock  resting  on  dioritic  and  granitic 
masses,  and  none  of  the  lower  strata  developed  (pp.  73-7-1:). 

WiNCHELL,  N.  H.     The  origin  of  the  Archean  greenstones:  Twenty-third  Ann. 
Rept.  Minnesota  Geol.  and  Nat.  Hist.  Survey  for  1894,  pp.  4-35.     1895. 

The  author  again  (see  p.  101)  turns  to  the  subject  of  the  origin  of  the 
greenstones  in  the  Lake  Superior  region.  He  begins  his  article  with  a  mis- 
statement of  the  conclusions  reached  by  Williams  in  his  discussions  of  the 
Menominee  and  Marquette  green  schists,  asserting  that  "the  tendency  of 
the  conclusions  reached  by  Dr.  Williams  is  to  refer  the  greenstones  as  a 
body  to  dynamic  metamorphism  of  massive  irruptive  rocks"  (p.  4).  The 
object  of  the  present  paper  is  to  give  the  reasons  of  the  author's  present 
belief  "that  the  great  bulk  of  the  'greenstones'  as  an  Archean  terrane 
ought  to  be  classed  as  pyroclastic,  i.  e.,  that  they  originated  from  eruptive 
agencies,  as  tufi"  and  all  kinds  of  volcanic  dtibris,  sometimes  very  coarse, 
and  were  distributed  and  somewhat  stratified  by  the  waters  of  the  ocean 
into  which  the  materials  fell"  (p.  5).  The  main  point  of  Professor  Winchell's 
paper  seems  to  be  a  criticism  of  Williams  for  not  spreading  his  conclusions 
respecting  the  origin  of  the  Marquette  and  Menominee  greenstones  over 
the  greenstone-schists  of  the  entire  Lake  Superior  district,  and  for  not 
recognizing  tuffs  among  the  Menominee  rocks,  although  he  distinctly 
regarded  the  latter  as  of  surface  origin.  Winchell  again  criticises  Wil- 
liams's explanation  of  the  cross  gashes  in  the  hand  specimen  figured  by 
him,  and  declares  that  the  schistosity  of  the  Menominee  greenstones  is  not 


112  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

always  an  effect  of  pressure  and  shearing.  (See  pp.  94-98.)  The  author 
argues  against  the  general  conclusion  that  the  phenomena  observed  in  these 
rocks  are  due  principally  to  dynamic  metamorphism,  but  in  doing  so  he  mis- 
interprets many  of  Williams's  statements,  and  evidently  puts  meanings,  into 
them  that  they  were  never  intended  to  convey.  Everywhere  the  author 
argues  against  the  "irruptive  hypothesis"  for  the  greenstones,  presumably 
supposing  that  this  was  Williams's  hypothesis,  whereas  it  was  in  reality 
mainly  an  eruptive  hypothesis.  The  only  fault  that  the  present  paper 
really  shows  to  exist  in  Williams's  work  is  the  neglect  of  the  latter  to 
observe  the  fragmental  structure  of  certain  greenstones  in  the  neighborhood 
of  the  Little  and  the  Big  Quinnesec  Falls,  and  this  neglect  had  already 
been  referred  to  before  by  Wadsworth.  Professor  Winchell  finally  agrees 
with  Williams  that  the  present  condition  of  the  greenstone-schists  is  due  to 
dynamic  metamorphism,  although  he  does  not  distinctly  say  so.  He 
emphasizes  the  fact  that  the  i-otted  condition  of  the  schists  is  due  to 
weathering,  a  fact  which  Williams  also  admits. 

The  paper  concludes  with  a  discussion  of  "the  greenstones  as  a 
geological  terrane,"  but  the  discussion  is  mainly  with  respect  to  these  rocks 
in  Mimiesota,  a  subject  with  which  we  are  not  here  concerned. 

Van  Hise,  C.  R.,  and  Bayley,  W.  S.  Preliminary  report  on  the  Marqviette 
iron-bearing-  district  of  Michigan,  including  a  chapter  on  the  Republic  Trough  by 
H.  L.  Smyth:  Fifteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  Chap.  V,  pp.  631-650. 
1895. 

In  his  discussion  of  the  general  geology  of  the  Marquette  district 
Van  Hise  correlates  the  Lower  Marquette  series  with  the  Lower  Menominee 
of  Smyth.  He  places  the  succession  as  follows,  attempting  no  correlation 
between  the  upper  series: 

Upper  Marquette.  Upper  Menominee. 

Unconformity. 

Lower  Marquette.  Lower  Menominee. 


Negaunee  iron  formation,  1,000  to  1,500  feet {^ate-i  te^rTn  ^ric 


1  jasper. 
!  bearing  rich  ores 
Siamo  slate,   in  places  including  interstratified 

amygdaloids,  200  to  62.5  feet  thick 

Ajibik  quartzite,  700  to  900  feet 

Wewe  slate,  550  to  1,050  feet 

Kona  dolomite,  550  to  1,375  feet '.Crystalline  dolomite,  700  to  1,000  feet. 

Mesnard  quartzite,  100  to  670  feet Basal  quartzite,  700  to  1,000  feet. 


Slates  and  altered  volcanics,   maximum   thickness, 
2,000  feet. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  118 

The  succession  for  the  lower  series  would  thus  be  verj'  closelj^  parallel  in  the 
two  districts,  with  the  following  exceptions: 

(1)  The  Wewe  slate,  the  Ajibik  quartzite,  and  the  Sianio  slate  are  placed 
opi)osite  one  member  of  the  Menominee  series.  These  three  formations  are, 
however,  all  fragmental,  and  are  equated  with  a  fragmental  formation.  Together 
they  mark  a  time  of  mechanical  deposition  in  each  district  between  the  nonfrag- 
mental  limestone  and  the  nonfragmental  iron  formation,  and  thus  include  the 
physical  change  involved  in  passing  from  a  nonfragmental  to  a  fragmental,  and  then 
again  to  a  nonfragmental  formation.  The  chief  diflference  is  that  in  the  Marquette 
district  two  layers  of  mud  were  separated  by  a  layer  of  sand.  Another  difference 
is  that  in  the  Menominee  district  volcanics  are  much  more  important,  and  this  may 
account  for  the  absence  of  conditions  favorable  to  sand  deposits.  However,  it  is 
interesting  to  note  that  amygdaloids  are  found  in  the  Lower  Marquette  series  in  the 
Siamo  slate — that  is,  toward  the  higher  part  of  this  great  fragmental  formation. 
The  Fence  River  volcanics  in  the  Michigamme  district  occupy  a  similar  horizon. 

(2)  The  pure,  nonfragmental  iron  formation  of  the  Mai'quette  district  is  equated 

with  slates  bearing  the  rich  ores  of  the  Menominee  district  and  the  Michigamme 

jasper.     The  only  substantial  difference,  however,  is  that  in  the  Menominee  and 

Michigamme  districts  both  the  slates  and  the  jasper  bear,  with  the  nonfragmental, 

a  considerable  amount  of  fi'agmental  material.     In  other  words,  the  conditions  in 

these  districts  were  not  favorable  to  pure  nonclastic  sediments  as  they  were  in  the 

Marcjuette  district  [p.  649]. 

1896. 

Van  Hise,  C.  R.  Summary  of  pre-Cambrian  North  American  literature:  Jour. 
Geol.,  vol.  4,  pp.  748-750.     1896. 

The  author,  commenting'  upon  Smyth's  article  on  the  relations  of  the 
Lower  Menominee  and  the  Lower  Marquette  series,  declares  that  additional 
evidence  seems  to  be  necessary  to  prove  that  the  iron-bearing  slates  of  the 
Menominee  district  are  the  equivalents  of  the  slates  associated  with  the 
eruptives  farther  north.  If  these  are  not  equivalent,  the  Michigamme 
jasper  and  these  iron-bearing  slates  are  the  equivalents  of  the  iron-bearing 
formation  and  the  quartzite  below  it  in  the  Marquette  district,  in  which 
case  the  iron-bearing  horizon  of  the  Menominee  may  have  an  equivalent  in 
the  Marquette  district. 

Van  Hise,  C.  R.  Summary  of  the  pre-Cambrian  North  American  literature: 
Jour.  Geol.,  vol.  4,  pp.  753-754.     1896. 

In  criticism  of  WinchelVs  conclusions  that  the  greenstone-schists  of 
the  Lake  Superior  region  constitute  a  single  terrane,  and  that  the  bulk  of 
them  are  pyroclastic,  Van  Hise  declares  that  south  of  Lake  Superior  they 

MON  XLVI — 04 8 


114  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

constitute  three  distinct  terranes  in  three  distinct  and  unconformable  series. 
Some  of  them  are  pyroclastic,  some  are  extrusive,  and  some  are  intrusive 
in  origin. 

Newett,  George  A.    Mines  and  Mineral  Statistics,  pp.  47-62.    With  map.    1896. 

This  is  the  report  of  the  commissioner  of  mineral  statistics  for 
Michigan.  So  far  as  the  Menominee  district  is  concerned,  it  consists  prin- 
cipally of  a  description  of  the  condition  of  the  various  mines  in  the  district. 
The  map  is  an  outline  map  showing  the  location  of  the  23rincipal  mines  on 
the  range.  Several  sections  tlu-ough  the  Aragon  mine  and  two  tln-ough  the 
Pewabic  accompany  the  report.  The  longitudinal  section  through  the  Pewa- 
bic  mine  exhibits  the  distribution  of  the  high  and  the  low  phosphorus  ores. 

Birkinbine,  John.  Iron  ores:  Seventeenth  Ann.  Rept.  U.  S.  Geol.  Survey, 
pt.  3,  pp.  23-43.     With  maps.     1896. 

The  report  of  Birkinbine  is  almost  wholly  statistical.  It,  however, 
contains  several  maps  of  interest,  one  of  which  exhibits  the  location  of  the 
active,  suspended,  and  abandoned  mines  in  the  Menominee  district. 

W.  S.  Gresley.  Organic  markings  in  Lake  Superior  iron  ores:  Science,  n.  s., 
vol.  3,  pp.  622-623.     1896. 

The  author  announces  the  discovery  of  markings  resembling  traces  left 
by  organisms  in  fragments  of  iron  ore  from  the  Chapin  mine.  Iron  Mountain. 
The  specimens  showing  the  markings  were  picked  up  from  the  ore  piles  on 
the  docks  at  Erie,  Pa.  They  were  submitted  to  Messrs.  H.  S.  Williams,  of 
Yale;  Charles  Schuchert  and  C.  D.  Walcott,  of  Washington;  and  C.  R.  Van 
Hise,  of  the  University  of  Wisconsin.  Some  of  them  were  pronounced  by 
these  gentlemen  to  be  very  similar  to  the  trails  left  by  worms  in  mud  rocks. 

[WiNCHELL,  N.  H.]  Supposed  pre-Taconic  organisms:  Am.  Geologist,  vol.  18, 
pp.  123-124.     1896. 

Professor  Winchell  refers  to  the  above  note  by  Gresley  in  an  editorial 
in  which  he  declares  that  while  the  markings  may  be  of  organic  origin,  they 
will  nevertheless  "not  be  admitted  as  a  demonstration  of  Archean  life 
without  a  many-sided  scrutiny,  the  more  as  all  other  similar  claims  seem 
to  be  so  rapidly  crumbling." 

Van  Hise,  C.  R.  Principles  of  North  American  pre-Cambrian  geology: 
Sixteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  2,  pp.  743-843.  With  maps  and 
illustrations.     1896. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  115 

The  major  portion  of  this  article  is  a  discussion  of  the  relations  existing 
between  the  different  rock  series  in  North  America  that  are  of  pre-Cambrian 
age.  Among  others,  the  Lake  Superior  region  is  discussed,  but  no  special 
description  is  given  of  the  Menominee  district,  although  mention  is  made  of 
it  in  several  places.  The  Huronian  in  this  district  is  divided  into  the 
Upper  and  the  Lower  Menominee  series,  the  latter  of  which  is  in  general 
equivalent  to  the  Lower  Marquette  series,  the  corresponding  members  in 
the  two  being  as  follows: 

Lou'er  Mnrqaette.  Lower  Menominee. 

Negaunee  iron  formation,  1,000-1,500  feet.  Slates  bearing  rich  ores. 
Siamo  slate,  including  interstratified  amygdaloids,     Michiganinie  jasper. 

200-625  feet.  ,  Slates  and  altered  acid  and  basic  volcanics,  maxi- 

Ajiliik  quartzite,  700-900  feet.  mum  thickness,  2,000  feet. 

Wewe  slate,  5.50-1,000  feet.  Crystalline  dolomite,  700-1,000  feet. 

Kona  dolomite,  5.50-1,375  feet.  Basal  quartzite,  700-1,000  feet. 
Mesnard  quartzite,  100-670  feet. 

1897. 

Van  Hise,  C.  R.,  and  Bayley,  W.  S.  The  Marquette  iron-bearing  district  of 
Michigan,  with  atlas,  including  a  cliapter  on  the  Republic  Trough,  by  H.  L.  Sun-th. 
Mon.  U.  S.  Geol.  Survey,  vol.  28,  pp.  575-579.     1897. 

In  this  volume  the  same  discussion  is  given  concerning  the  correlation 
of  the  Menominee  and  the  Marquette  rocks  as  is  found  in  the  preliminary 
account  of  the  Marquette  district,  pubhshed  by  the   same  authors  in  1895. 

Gresley,  W.  S.  Traces  of  organic  remains  from  the  Huronian  (i)  series  at 
Iron  Mountain,  Mich.,  etc.:  Trans.  Am.  In,st.  Min.  Eng.,  vol.  26,  pp.  527-534.     1897. 

This  article  contains  descriptions  of  the  fossil  markings  the  discovery 
of  which  was  announced  by  the  author  in  1896  (p.  114).  For  several  years 
the  ore  piles  on  the  docks  at  Erie,  Pa.,  had  been  industriously  examined 
with  the  view  to  discovering  fossils  that  might  be  present  in  the  ores. 
Since  no  ores  are  used  at  Erie  except  those  of  the  Lake  Superior  region,  it 
appears  probable  that  the  specimens  obtained  came  from  this  reo'ion.  On 
the  authority  of  the  dock  superintendent  the  majority  of  the  specimens 
described  in  the  article  are  declared  to  have  originated  in  the  Chapin 
mine,  at  Iron  Mountain.  The  markings  are  of  various  kinds,  most  of  the 
varieties  being  represented  by  drawings  on  four  plates.  Of  those  thus 
represented  some  are  thciught  to  be  the  impressions  of  plants,  others  of 
corals,  and  others  of  footprints.     The  greatest  number  are  thought  to  be 


116 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


trails   left  by  crawling  animals.     One    specimen  resembles   the    mold   of 
sun  cracks.     The  best  characterized  of  these  markings  are  reproduced  as 

Pis.  VI  and  VII. 

1899. 

Clements,  J.  Mokgan,  and  Smyth,  Henry  Lloyd.  The  Crystal  Falls  iron- 
liearing  district  of  Michigan;  with  a  chapter  on  the  Sturgeon  River  tongue,  by 
William  Shirlej^  Bayley,  and  an  introduction,  bj'  Charles  Richard  Van  Hise:  Nine- 
teenth Ann.  Rept.  U.  S.  Geol.  Survey,  pt.  3;  pp.  1-151.  With  2  maps,  9  plates, 
and  6  illustrations  in  text.     1899. 

In  his  introduction  to  this  report  Van  Hise  correlates  the  formations  of 
the  Marquette,  Crystal  Falls,  and  Menominee  districts  as  follows: 


Marquette  District. 
Upper  Marquette  series. 

(1)  Michiganime  formation, 
bearing  a  short  distance 
above  its  base  an  iron- 
bearing  horizon,  and  being 
replaced  in  much  of  the 
district  by  the  Clarksburg 
volcanic  formation. 

(2)  Ishpeming  formation, 
composed  of  the  Goodrich 
quartzites  in  the  eastern 
part  of  the  district  and  of 
the  Goodrich  quartzite  and 
the  Bijiki  schists  in  the 
western  part  of  the  district. 


Crystal  Falls  District. 

Upper  Huronian. 

(1)  Michigamme  formation,' 
bearing  a  short  distance 
above  its  base  an  iron- 
bearing  horizon. 


(2)         Quartzite  in  eastern  part 
of  district. 


f(l) 


Meno.minee  Distkict. 
Upper  Menominee. 
Great  slate  formation. 


(Unconformity. ) 

(Unconformity.) 

(Unconformity.) 

Lower  Marquette  series. 

Lower  Huronian. 

Lo^i'er  Menominee. 

( 1 )        Negaunee  iron  formation,     ( 1 ) 

The     Gioveland    forma- 

(1)        Vulcan    iron    formation. 

1,000  to  1,500  feet. 

tion,  about  500  feet  thick. 

containing  slates. 

(2)        Siamo    slate,    in    places 

(2) 

Hemlock  volcanic  forma- 

including       interstratified 

tion,    1,000   to    10,000   feet 

amygdaloids,  200  to  625  feet 

thick.     In  western  part  of 

thick. 

district    also    occupies  the 

(3)        Ajibik   quartzite,   700  to 

place  of  (1)  and  (3). 

(2)        Antoine  dolomite. 

900  feet. 

(4)        AVewe  slate,  550  to  1,050 

(3) 

Mansfield  formation,  100 

feet. 

to  1,900  feet  thick. 

(5)         Kona    dolomite,    550    to     (4) 

Randville  dolomite,   500 

1,375  feet. 

to  1,500  feet  thick. 

(6)        ]Mesnard  quartzite,  100  to     (5) 

Sturgeon  quartzite,  100  to 

(3)        Sturgeon  quartzite. 

670  feet. 

1,000  feet  thick. 

(Unconformity.) 

(Unconformity.) 

(Unconformity.) 

Archean. 

Archean. 

Archean. 

PLATE   VI. 


117 


PLATE    VI. 

ORGANIC   MARKINGS   IN    THE    LAKE    SUPERIOR   IRON    ORES.       AFTER   GRESLET. 

Fig.  1. — Probably  remains  of  marine  plants  or  corals  (?).  Oldhamia  (?).  On  a  thin  layer  of 
isoftish,  fine-grained,  sandy,  purplish  iron  ore.  Locality,  Chapin  mine.  Iron  Mountain,  Mich.  Mag- 
nified two  diameters. 

Fig.  2. — Shows  roughly-parallel  rows  of  small,  shallow  depressions;  some  plant  (?),  or  possibly 
flattened  tracks  of  some  crawling  animals,  on  the  surface  of  a  layer  or  band  of  red,  earthy  iron  ore. 
Locality  uncertain. 

Fig.  3. — Perhaps  casts  of  remains  of  plant  stalks.  On  the  surface  of  a  fragment  of  purplish-red 
,ore.     Locality  uncertain,  but  the  same  as  that  of  fig.  2. 

Fig.  4. — Perhaps  fiUed-up  sun  cracks.  Occurring  as  ridges  on  laminse  of  a  fragment  of  soft,  blue 
iron  ore.     Locality  unknown,  but  the  same  as  that  of  figs.  2  and  3. 

Fig.  5. — Perhaps  the  imprint  of  the  cast  or  mold  of  a  fragment  of  a  marine  plant.  On  the  sur- 
face of  softish  lamina;  of  red  hematite.     Locality  unknown. 

118 


U.    S.   GEOLOGICAL   SURVEY 


MONOGRAPH    XLVI       PL.    VI 


f',  n 


^v. 


4  '5 

ORGANIC    MARKINGS    IN   THE    LAKE   SUPERIOR    IRON    ORES.     AFTER   GRESLEY. 


«r- 


PLATE   VII. 


119 


PLATE     VII. 

ORGANIC    MARKINGS    IN    THE    LAKE    SUPERIOR   IRON    ORES — AFTER   GRESLEY. 

Fig.  1.— Tracks  of  crawling  animals  on  nearly  flat  surface  of  a  slab  of  bluish-purple  laminaj  of 
sandy  iron  ore.  Note  the  parallelism  of  these  tracks.  The  grooves  running  diagonally  across  them 
may  have  been  made  by  plants  scraping  over  the  bottom  of  the  sea  or  lake.  Locality,  Chapin  mine, 
Mich. 

Fig.  2. — A  few  individual  footprints  of  1,  enlarged  four  times. 

Fig.  3.— Possibly  plant  remains,  or  animal  traclis  (?)  apparently  somewhat  side  squeezed.  On  a 
surface  of  a  fragment  of  a  band  of  fine-grained  purplish-red  iron  ore.  On  the  reverse  or  opposite  side 
of  this  specimen  (which  is  aliout  three-fourths  inch  thick)  are  very  uniform  parallel  strire  of  fine 
grooves,  very  suggestive  of  flattened  bark  or  riljbed  plant  structure.  Locality,  Chapin  mine,  Iron 
Mountain,  Mich. 

Fig.  4.— Probably  track  of  some  crawling  animal.  Upon  a  bedding  plane  of  a  bit  of  soft,  sandy, 
purplish  iron  ore.     Locality  uncertain. 

Fig.  5." — About  one-eighth  of  tlie  surface  of  one  side  of  a  fragment  of  soft,  bluish,  fine,  sandy  iron 
ore,  exhibiting  side-squeezed  (?)  or  distorted  animal  footprints  (?),  distorted  rain  spots  (?),  or  shriveled 
plant  remains  (?).     Locality  uncertain. 

Fig.  6. — Possibly  a  bit  of  a  marine  plant.  On  the  surface  of  purplish  lamina^  of  ore.  Locality, 
Chapin  mine  (?),  Iron  Mountain,  IMich. 


"Compare  with  this  parts  of  figs.  1  and  2  of  PI.  VI. 

120 


U.   S.   GEOLOGICAL   SURVEY 


MONOGRAPH    XLVI       PL.    Vlt 


ORGANIC    MARKINGS    IN    THE   LAKE  SUPERIOR    IRON    ORES.     AFTER   GRESLEY. 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  121 

He  states  that  in  the  Menominee  district  there  appears  to  be  no  quartz- 
ite  at  the  base  of  the  Upper  Huronian  coi'responding  to  the  Ishpeming 
quartzite  in  the  Marquette  district,  nor  is  there  in  the  former  district  any 
great  volcanic  formation  corresponding  to  the  Clarksburg  formation  of  the 
Marquette  area.  The  Lower  Huronian  formations  in  the  three  districts  are 
practically  parallel,  except  for  the  volcanic  deposits  in  the  Crystal  Falls 
district. 

The  distribution  of  the  formations  in  the  three  districts  indicates  that 
the  transgression  of  tlie  Huronian  sea  was  from  the  southeast  toward  the 
northwest;  the  Menominee  area  having  been  submerged  before  the  central 
portion  of  the  Crystal  Falls  district  and  the  western  part  of  the  Marquette 
district.  Practically  the  same  view  is  expressed  by  Smyth  in  Chapter  V 
of  the  report  (pp.  140-145),  as  the  result  of  magnetic  observations  west  of 
Republic. 

Clements,  J.  Morgan,  and  Smyth,  Henry  Lloyd.  The  Crystal  Falls  iron- 
bearing  district  of  Michigan,  with  a  chapter  on  the  Sturgeon  River  tongue,  by  Wiu. 
Shirley  Bayley,  and  an  introduction  by  Charles  Richard  Van  Hise:  Mon.  U.  S. 
Geol.  Survey,  vol.  36.     With  13  maps,  36  plates,  and  24  figures  in  the  text.     1899. 

This  report  contains  a  more  detailed  account  of  the  geology  of  the 
Crystal  Falls  district  than  that  referred  to  in  the  immediately  preceding 
paragraphs.  So  far  as  the  Menominee  district  is  concerned,  it  contains 
practically  the  same  statements  as  the  preceding  article. 

Newett,  George  A.     Mines  and  Mineral  Statistics  of  Michigan.     1899. 

The  annual  statistical  and  mine  report  of  the  commissioner  of  mineral 
statistics  for  Michigan  contains  the  usual  statistics  of  the  Menominee  and 
other  ore  districts  and  items  of  interest  concerning  the  mines. 

1900. 

Van  Hise,  C.  R.,  and  Bayley,  W.  S.  Description  of  Menominee  district: 
Geologic  Atlas  U.  S.,  folio  62,  U.  S.  Geol.  Survey.  With  geologic  and  topographic 
maps.     1900. 

This  is  a  preliminary  report  on  the  geology  of  the  Menominee  district. 
Its  conclusions  are  practically  the  same  as  those  embodied  in  the  present 
monograph,  of  which  it  is  actually  a  summary.  The  geological  map  is  less 
complete  than  that  accompanying  the  present  volume,  since  several  areas 
on  the  former  were  left  without  the  color  of  any  of  the  formations  of  the 
district  because  of  lack  of  evidence  as  to  the  nature  of  the  underlying  rock. 


122 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


The   correlation  of  the  various  formations   in  the   different  iron-ore 
districts  on  the  south  side  of  Lake  Superior  is  given  as  follows: 

Descending  succession  in  the  Penokee^  Marquette^  Crystal  Falls ^  and  Menominee 

districts. 


Penokee  District. 

Lake  Superior  sandstone. 

(Unconformity.) 
Keweenaw  series. 
{Unconformity.) 

Upper  Huronian. 


1.  Upper  slate  member. 

2.  Iron-bearing  member. 
(In  east  part  of  the  dis- 
trict volcanic  f  ragmentals 
are  associated  with  1  and 
2.) 

3.  Quartz-slate        member, 
having — 

(a)  A  thin  belt  of  quartz- 
ite  at  its  top; 

(b)  A  main  belt  of  slate 
below;  and 

{c)  A  thin  belt  of  quartz- 
ite  at  its  bottom  at  vari- 
ous localities. 

(Unconformity. ) 

Lower  Huronian, 

(Evidence  of  the  former 
existence  of  an  iron-bear- 
ing member  above  the 
cherty  limestones  is  seen 
in  the  presence  of  ore  and 
jaspilite  grains  in  basal 
portion  of  quartz-slate 
member. 
1.  Cherty  limestone  mem- 
ber. 


(Unconformity.) 

Archea7i. 


Marquette  District. 
Lake  Superior  sandstone. 

(Unconformity.) 

Upper  Huronian. 

1.  Michigamme  formation 
(locally  replaced  by 
Clarksburg  volcanic  for- 
mation). 

One    might    divide    the 
Michigamme      sedimen- 
tary formation  into  three 
members: 
(a)  Upper  slate  member. 


(b)  Iron-bearing  member.     2. 


(c)  Lower  slate  member. 

Ishpeming  formation  of 
quartzites  and  detrital 
ores,  and  the  Bijikl 
schists  in  western  part  of 
district. 


Crystal  Falls  District. 
Lake  Superior  sandstone. 


(Unconformity.) 

Lower  Huronian. 


1.    Negaunee 
formation. 


iron-bearing 


Siamo  slates,  containing 

interstratified      amygda- 

loids. 

Ajibik  quartzite. 

Wewe  slate. 

Kona  dolomite. 


6.    Mesnard  quartzite. 
(Unconformity.) 
Archean. 


(Unconformity.) 


Upper  Huronian. 

Michigamme  formation 
(consists  of  three  mem- 
bers equivalent  to  those 
of  the  Marquette  district, 
but  2  and  3  given  below 
can  be  separated  in  map- 
ping only  in  the  southern 
part  of  the  district). 


Groveland     iron-bearing 

formation    in     southern 
part  of  district. 


3.    Mansfield  slate. 


(Unconformity.) 

Lotver  Huronian. 

1.  Negaunee  iron-bearing 
formation  in  northeast- 
ern part  of  district. 

2.  Hemlock  volcanic  forma- 
tion. 

3.  Randville  dolomite. 


4.    Sturgeon  quartzite. 
(Unconformity.) 

Archean. 


Menominee  District. 
Lake  Superior  sandstone. 

(Unconformity.) 

Upper  Huronian. 


Han  bury  slate,  bearing 
in  lower  portion  calcare- 
ous slates,  etc.,  contain- 
ing siderite. 

Vulcan  formation  con- 
sisting in  descending 
order  of — 

(a)  Curry  iron-bearing 
member. 


(h)  Brier  slate. 

(c)  Traders  iron-bearing 

member. 


(Unconformity.) 

Lower  Huronian. 

1.    Negaunee      iron-bearing 
formation. 


2.    Randville  dolomite. 


3.    Sturgeon  quartzite. 
(Unconformity.) 

Archean. 


In  the  table  it  will  be  noted,  by  comparing  the  column  given  for  the  Crystal 
Falls  district  with  that  contained  in  Monograph  XXXVI  of  the  United  States 
Geological  Survey,  that  the  succession  has  been  somewhat  changed.  When  the 
monograph  was  published,  it  was  supposed  that  the  Groveland  iron  formation  and 
the   Mansfield   slate   of   the   southern  part  of   the  district  belong   in   the   Lower 


BIBLIOGRAPHY  AND  ABSTRACT  OF  LITERATURE.  123 

Huronian ;  but  the  work  in  the  Menominee  district  shows  bej^ond  reasonable 
question  that  these  formations,  which  have  a  comparative!}'  small  areal  extent  in 
the  Crystal  Falls  district,  really  belong  in  the  Ujijier  Huronian. 

Discrepancies  in  columns. — In  the  four  districts  the  correlation  of  the  series 
placed  opposite  one  another  and  separated  by  the  unconformities,  and  the  correla- 
tion of  the  unconformities,  may  be  regarded  as  practically  certain  ;  also  the  cor- 
relation of  individual  members  within  the  parallel  series  has  in  many  cases  a  very 
high  degree  of  probability.  However,  an  examination  of  the  table  shows  various 
discrepancies.  These  discrepancies  are  due  in  a  given  case  to  one  or  more  of  the 
following  causes : 

During  the  time  a  series  or  formation  was  being  deposited  throughout  all  or 
a  part  of  one  district,  all  or  a  part  of  another  district  was  still  undergoing  erosion. 
As  the  sea  advanced  overlap  resulted.     *     *     * 

The  inter-Huronian  erosion  cut  to  different  depths  in  the  different  districts, 
as  a  consequence  of  which  formations  of  the  Lower  Huronian  may  have  been 
largely  removed  in  one  district  and  may  have  been  comparativelj'  untouched  in 
another.     *     *     * 

A  formation  may  have  a  greater  vertical  range  in  one  district  than  in  another; 
the  conditions  may  have  remained  uniform  in  one  district,  and  therefore  deposits 
of  the  same  kind  continued,  while  the  conditions  changed  in  another  district,  and 
therefore  more  than  one  formation  was  deposited.  *  *  *  Xhe  order  of  forma- 
tions in  the  Upper  Huronian  might  at  first  thought  be  regarded  as  very  different  in 
the  various  districts.  However,  if  one  reduces  the  order  of  succession  to  a  general 
statement,  it  is  as  follows:  (1)  An  upper  fragmental  slate  member;  (2)  an  iron- 
bearing  member,  largely  nondetrital;  and  (3)  a  lower  fragmental  member,  which 
consists  of  quartzites,  slates,  and,  at  its  base  in  some  districts,  large  quantities  of 
fragmental  iron-formation  material. 

*  »  *  *  *  *  * 

The  attempt  to  correlate  the  various  formations  of  the  two  Huronian  series 
in  the  four  different  iron-bearing  districts  south  of  Lake  Superior  shows  very 
significantly  that  the  geologic  history  of  pi'e-Cambrian  time  was  extraordinarily 
complex.  From  Archean  to  Cambrian  time,  in  the  Marquette,  Crystal  Falls,  and 
Menominee  districts,  the  areas  three  times  emerged  from  the  sea  and  were  three 
times  overridden  bj'  the  sea.  In  the  Penokee  district  there  was  a  fourth  emergence 
and  transgression  of  the  sea.  The  epeirogenic  or  land-making  movements  were 
accompanied  by  orogenic  movements,  or  mountain  growths,  of  varying  power, 
but  some  of  them  exceedingly  intense.  In  Huronian  time,  in  all  the  districts 
except  the  Menominee,  there  were  important  and  long-continued  periods  of  vol- 
canism.  The  great  events  of  Keweenawan  time  are  only  mentioned,  since  they 
do  not  particularly  concern  the  Menominee  district.  The  erosive  forces  at  periods 
when  the  districts  were  land  areas  found  rocks  of  veiy  different  characters.  Here 
thej'   were   resistant;   there   easilj'  denuded.      As    a    consequence,    when    the    sea 


124  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

encroached  at  the  close  of  Archean,  Lower  Huronian,  and  Upper  Huronian  times, 
the  country  in  detail  was  very  irregular — was,  in  fact,  bluily,  but  not  mountainous. 
Therefore  certain  areas  were  covered  b}-  the  sea,  while  other  immediateh'  adjacent 
areas  were  above  the  water  and  were  being  actively'  eroded.  As  a  consequence  of 
all  these  complex  conditions  we  have  unconformity,  overlap,  changes  in  the 
chai'acters  of  contemporaneous  sediments  along  the  strike  and  across  the  strike, 
disturbances  in  the  successions  due  to  volcanism,  close  folding  and  attendant 
metamorphism,  and  all  of  these  phenomena  in  a  region  which  is  largely  covered  by 
glacial  drift. 

Van  Hise,  C.  R.  The  iron-ore  deposits  of  the  Lake  Superior  region:  Twenty- 
lirst  Annual  Rept.  U.  S.  Geol.  Survey,  pt.  3,  with  maps  and  other  illustrations. 
The  Menominee  district,  pp.  388-100.     1901. 

In  this  paper  Van  Hise  gives  a  summary  of  the  facts  known  concern- 
ing the  geology  of  the  various  iron-ore  producing  districts  in  the  Lake 
Superior  region,  and  a  brief  discussion  of  the  processes  that  resulted  in  the 
deposition  of  the  ores. 

The  account  of  the  Menominee  district  is,  in  the  main,  abstracted  from 
the  preliminary  report  on  the  district  by  Van  Hise  and  Bayley  (see  p. 
121).  The  development  of  the  Menominee  ores  is  said  to  combine  the 
features  that  characterize  the  development  of  the  ore  deposits  that  occur  in 
the  Penokee-Gogebic  and  the  Marquette  districts.  The  occm-rence  of  the 
ore  bodies  is  declared  to  be  in  practically  every  case  on  the  lower  portions  of 
slopes ;  that  is.  at  the  places  where  descending  waters  have  been  converged 
from  a  wide  variety  of  sources.  The  time  of  the  concentration  must  have 
been  after  the  folding  which  produced  the  troughs  in  the  district  and  after 
the  period  of  erosion  which  removed  the  Hanbury  slates  that  once  covered 
the  ore  formations;  that  is,  in  the  interval  between  Upper  Hiironian  and 
Upper  Cambrian  times. 

The  map  of  the  Menominee  district  accompanying  the  paper  is  a 
reproduction  of  that  published  in  folio  62  of  the  Geologic  Atlas  of  the 
United  States. 


CHAPTER    III. 

PHYSIOGRAPHY. 

TOPOGRAPHY. 

The  Meuoniinee  district  is  but  a  small  portion  of  a  large  area,  which 
lies  between  Green  Bay  and  Lake  Superior  and  the  margin  of  the  valley 
of  the  Mississippi  River,  and  which  may  be  characterized  physiographically 
as  a  southeasterly  inclined  peneplain.  In  that  portion  of  the  area  dis- 
cussed in  the  following  pages  the  relief  is  strong,  though  in  no  sense 
mountainous.  The  highest  elevation  is  in  Hughitt  Bluff,  at  Iron  Moimtain, 
the  top  of  which  is  between  1,560  feet  and  1,580  feet  above  sea  level. 
The  banks  of  the  Menominee  River,  where  this  sti'eam  leaves  the  area, 
have  an  altitude  of  800  feet.  While  this  difference  in  height  is  only  760 
or  780  feet  the  slopes  of  the  elevations  are  comparatively  steep.  The 
heights  of  the  hills  are  thus  emphasized  and  the  surface  of  the  area  appears 
to  the  eye  much  more  rugged  than  it  actually  is  (see  map,  PI.  VIII). 

The  Huronian  trough,  or  the  Menominee  district  pi-oper,  as  has  been 
explained,  lies  between  the  Menominee  River  on  the  south  and  an  area  of 
granite  and  schist  knobs  on  the  north.  Its  surface  comprises  two  plains 
sloping  gradually  toward  the  southeast.  The  lower  one,  which  has  an  ele- 
vation of  about  1,000  feet  in  the  center  of  the  district,  gradually  rises  to 
1,200  feet  in  its  extreme  northwestern  portion  and  descends  to  about  900 
feet  in  its  extreme  southeast  corner.  It  also  inclines  southward  toward 
the  JMenominee  River  at  the  rate  of  about  25  feet  to  the  mile.  This  plain 
forms  the  valleys  between  the  residuals  of  the  higher  plain  which  constitute 
the  hills. 

The  higher  plain,  like  the  lower  one,  slopes  to  the  southeast.  In  the 
Avestern  portion  of  the  area  its  surface  is  at  an  elevation  of  about  1,500  feet, 
while  in  the  eastern  portion,  near  the  Stui'geon  River,  it  recedes  to  1,200 
feet.  Only  a  few  remnants  of  the  higher  plain  remain.  They  are  arranged 
in  two  series,  constituting  two  well-defined  ranges  of  hills  trending  a  little 

125 


126  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

south  of  east,  or  in  the  direction  of  the  prevailing  strike  of  the  Huronian 
rocks  composing  them.  In  nearly  every  instance  the  hills  consist  very 
largely,  if  not  exclusively,  of  the  hard,  vertical,  or  nearly  vertical,  Rand- 
ville  dolomite,  and  of  the  even  more  resistant  jaspilites  of  the  Vulcan  forma- 
tion, and  are  topped  by  the  horizontal  beds  of  the  Lake  Superior  sandstone. 
The  intervening  valleys  between  the  hills  are  underlain  mainly  by  the  soft 
slates  of  the  Hanbury  formation,  although  along  the  northern  border  of  the 
trough  the  valley  floor  may  extend  across  a  narrow  belt  of  the  Randville 
dolomite. 

The  plan  of  the  topography  thus  corresponds  very  closely  with  the 
geological  structure  of  the  district.  The  ridges  follow  the  strike  of  the 
more  resistant  rocks  and  end  where  these  pitch  beneath  the  overlying 
softer  slates.  The  valleys  occupy  the  synclines  of  slate  between  the  anti- 
clines of  the  harder  rocks  and  open  out  toward  the  west  to  correspond  with 
the  widening  out  of  westward-pitching  synclines  of  the  softer  rocks.  Glacial 
deposits  have  modified  to  some  extent  the  perfection  of  the  plan,  but  they 
have  not  affected  the  topography  greatly,  except  in  the  northwest  corner 
of  the  area,  where  high  and  irregularly  shaped  sand  hills  constitute  all  the 
elevations. 

DRAINAGE. 

The  area  is  drained  by  two  longitudinal  streams,  the  Menominee  River, 
where  it  borders  the  area  on  the  south,  and  Pine  Creek,  and  by  two  cross 
streams.  The  latter  are  the  Menominee  River,  where  it  borders  the  area 
on  the  west,  and  the  Sturgeon  River  near  its  eastern  side. 

The  major  streams  traversing  the  district — the  Menominee  and  the 
Sturgeon  rivers — are  both  apparently  antecedent.  They  both  cross  the 
hard  rock  beds  transversely  to  their  strike  and  flow  through  gorges  over 
cataracts  and  rapids.  The  Menominee  River  shows  its  disregard  of  the 
geological  structure  by  cutting  iudiff'erently  through  crystalline  greenstones 
and  soft  sand  and  clay  deposits.  Along  the  southern  side  of  the  district  its 
meanders  wind  in  and  out  of  the  green  schist  area,  always  keeping  near  the 
boundary  between  the  schists  and  the  Hanbury  slates.  Where  the  stream 
enters  and  leaves  the  schist  area  there  are  falls,  and  within  the  area  its 
channel  is  marked  by  many  small  cascades  and  rapids  (see  pp.  132-133). 

The  Sturgeon  River  enters  the  district  near  its  northeast  corner  and 
flows   across   it  for  a  distance  of  6  miles.     Where   its   channel  traverses 


ORIGIN  OF  THE  TOPOGRAPHY.  127 

the  quartzite  bordering  the  north  side  of  the  trough  is  one  of  the  most 
picturesque  and  wildest  gorges  in  the  Upper  Peninsula  of  Michigan.  This 
gorge  is  only  a  few  hundred  feet  in  length,  but  its  walls,  cut  in  snow- 
white  quartzite,  rise  almost  perpendicularly  above  the  bed  of  the  stream, 
confining  the  water  to  a  narrow  channel,  tlu-ough  which  it  rushes  with 
great  rapidity  over  several  little  cascades. 

The  principal  drainage  of  the  district  is  through  Pine  Creek,  which, 
though  small  in  volume,  extends  nearly  the  entire  length  of  the  trough.  It 
has  been  referred  to  above  as  a  longitudinal  stream;  and,  within  the  limits 
of  the  Menominee  district,  as  defined  in  the  preceding  chapter,  its  course  is 
longitudinal.  Just  beyond  the  boundary  of  the  area,  however,  it  crosses 
the  quartzite  belt  in  a  narrow  gorge,  known  as  the  "rock  dam"  (see  pp.  189- 
192),  where  it  is  transverse. 

The  stream  rises  some  distance  north  of  the  Menominee  area  and 
enters  the  district  from  the  north.  It  flows  south  for  a  few  miles  after 
entering  the  district  and  then  turns  to  the  southeast,  keeping  very  close  to 
the  base  of  the  quartzite  bluifs  forming  the  northern  side  of  the  Huronian 
synclinorium.  In  its  southeast  course  it  follows  a  belt  of  dolomite  lying 
south  of  the  quartzite  until  within  a  few  miles  of  its  mouth.  Here  it  crosses 
a  slate  valley  to  its  center  and  then  turns  abruptly  eastward  and  follows 
along  the  north  side  of  a  more  southerly  belt  of  dolomite  to  the  Loretto 
mine,  where  it  empties  into  the  Sturgeon  River.  Through  most  of  its 
course  its  bed  is  composed  of  sand  and  gravel,  and  nowhere  within  the 
confines  of  the  district  mapped  does  it  reach  the  underlying  rocks. 

ORIGIN  OF  THE  TOPOGRAPHY. 

It  appears  quite  evident  that  Pine  Creek,  with  its  present  small  volume 
of  water,  could  not  have  carved  the  large  valley  in  which  it  flows.  It  is 
also  plain  that  the  wide  valley  floors  with  the  residuals  of  a  higher  plain 
rising  above  them  could  not  have  been  the  result  of  the  action  of  the 
present  Menominee  River.  The  higher  ridges  are  much  nearer  the  channel 
of  this  river  than  they  are  to  the  channel  of  Pine  Creek.  Moreover,  there  is 
no  distinct  valley  on  both  sides  of  the  river  which  is  at  all  commensurate  in 
size  with  the  magnitude  of  the  river.  The  country  to  the  south  of  the  river 
has  not  been  mapped,  but  the  impression  gained  while  traveling  across  it  is 
to  the  effect  that  a  distinct  valley  is  lacking.     This  is  in  accord  with  the 


128  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

view  that  the  Menommee  is  in  its  present  position  a  new  stream  tiiat  has 
been  turned  from  its  old  course  by  recent  events. 

The  major  features  of  the  topography  of  the  district  not  only  antedate 
the  Glacial  epoch,  but  they  were  determined  before  Upper  Cambrian  time. 
Not  only  are  the  hills  of  the  region  capped  by  the  horizontal  Upper 
Cambrian  sandstone,  but  remnants  of  this  formation  have  been  found  in 
the  cross  gorges  at  Iron  Mountain,  Quinnesec,  and  Norway,  and  in  the 
longitudinal  valleys  at  several  places.  At  Iron  Hill  a  miniature  sandstone 
mesa,  with  perpendicular  sides  10  feet  high,  stands  near  the  banks  of  the 
little  stream  near  the  quarter  post  between  sees.  32  and  33,  T.  40  N., 
R.  29  W.  It  is  entirely  isolated  from  the  surrounding  rocks  and  is  plainly 
a  remnant  of  a  bed  that  once  completely  occupied  the  lowlands. 

Although  very  resistant  to  weathering  agencies,  the  sandstone  has, 
nevertheless,  been  almost  completely  removed  from  the  valleys,  while  it  has 
escaped  erosion  mainly  on  the  tops  of  the  ridges.  The  topogra^^liy  which 
has  resulted  from  the  removal  of  this  covering  is  therefore  very  similar  to 
that  which  characterized  the  surface  at  the  beginning  of  Upper  Cambrian 
time.  The  present  valleys  correspond  to  the  pre-Cambrian  vgjleys  and  the 
present  hills  to  elevations  that  existed  on  the  pre-Cambrian"  surface.  The 
floors  of  the  valleys  may  have  been  lowered  somewhat  since  the  sandstone 
disappeared,  but  since  the  bases  of  sandstone  remnants  are  in  several  widely 
separated  localities  either  at  the  present  valley  surfaces  or  only  a  few  score 
feet  above  them,  the  differences  in  elevation  between  the  pre-Cambrian 
valley  floors  and  those  of  the  present  valleys  can  not  be  great. 

The  present  topography  of  the  district  is  thus  mainly  resurrected  pre- 
Cambrian  topography.  It  had  its  origin  in  the  interval  between  Huronian 
and  Upper  Cambrian  times,  and  was  protected  until  very  recently  hj  the 
blanket  of  sand  laid  down  upon  it  by  the  Upper  Cambrian  sea.  If  erosion 
was  no  more  rapid  in  early  Cambrian  time  than  in  later  time,  the  interval 
between  Huronian  time  and  Upper  Cambrian  time  must  have  been  extremely 
long. 

"The  term  "pre-Cambrian"  is  here  used  to  cover  that  portion  of  time  antecedent  to  the  time 
represented  by  the  Lake  Superior  sandstone,  which  belongs  in  an  Upper  Cambrian  horizon.  Rocks  of 
Lower  and  of  Middle  Cambrian  age  have  not  yet  been  identified  in  the  Lake  Superior  region. 


ORIGIN  OF  THE  TOPOGRAPHY.  129 


PRE-CAMBRIAN    TOPOGRAPHY. 


The  pre-Cambrian  topograpby,  though  in  the  main  similar  to  that  of 
the  present,  nevertheless  differed  from  it  in  some  minor  respects.  The  hills 
of  the  earlier  period  were  not  so  lofty  as  those  now  existing,  but  they  were 
sharper  and  more  rugged.  Moreover,  both  hills  and  valleys  were  cut  by 
deep  and  narrow  gorges,  which  have  been  preserved  to  us  by  sandstone 
fillings.  The  Cuff  mine,  for  example,  is  situated  at  the  top  of  an  ancient 
north-facing  bluff,  for  the  sandstone,  which  forms  a  thin  covering  over  the 
surface  at  the  shaft,  is  found  again  at  considerable  depths  at  the  north  ends 
of  the  mine  levels.  Prospect  Bluff  was  narrower  in  these  earlier  times. 
Its  north  side  sloped  steeply  and  its  apex  was  shai-p.  A  deep  gorge  crossed 
Hughitt  Bluff  on  the  property  of  the  Pewabic  mine.  North  of  the  Quin- 
nesec  mine,  well  up  on  the  slope  of  a  high  hill,  was  formerly  a  deep  basin  in 
which  were  accumulated  bowlders  of  ore  and  hematite  sand  worn  from 
shores  carved  in  Huronian  rocks.  Finally,  drill  borings  have  shown  that 
a  deep  and  narrow  channel  crossed  the  plain  east  of  the  Norway  mine. 

The  surface  upon  which  the  sandstone  was  laid  down  was  then,  appar- 
ently, rougher  than  that  of  the  present  time,  although  in  their  major  features 
the  topography  of  the  pre-Cambrian  land  surface  and  that  of  tlie  present 
land  surface  were  similar.  The  presence  of  gorges  and  valleys  in  the 
pre-Cambrian  land  surface  at  places  where  they  do  not  now  exist  may 
explain  the  occurrence  of  ore  deposits  in  certain  positions  within  the 
Menominee  area  where  the  present  topographic  conditions  are  not  especially 
favorable  to  their  development  (see  p.  401). 

MON    XLVI — Oi- y 


CHAPTER   IV. 

THE   ARCHEAN    SYSTEM. 

The  sediments  composing  the  Menominee  trough  are  bordered  on  the 
north  for  nearly  their  entire  extent  by  a  complex  of  granites,  gneisses, 
hornblende-schists,  and  a  few  greenstone-schists  that  are  cut  by  dikes  of 
diabase  and  dikes  and  veins  of  granite.  This  has  been  designated  the 
Northern  Complex. 

On  the  south,  along  the  Menominee  River,  the  trough  is  bordered  by 
a  series  of  dark-green  or  black  basic  schists  and  light-colored  acid  schists, 
designated  hereafter  as  the  Quinnesec  schists.  These  are  cut  by  large 
dikes  of  gabbro,  diorite,  and  diabase;  by  smaller  dikes  of  granite,  quartz- 
porphj^ry,  and  felsite;  and  by  veins  of  quartz.  The  porphyries  and  many 
of  the  granite  dikes  are  apophyses  of  a  large  mass  of  granite  which  intrudes 
the  schists  and  constitutes  a  boss  whose  surface  occupies  hundreds  of  square 
miles  in  Wisconsin.  No  portion  of  this  boss  falls  witlihi  the  limits  of  the 
Menominee  district.  Its  northern  boundary  approaches  within  one-lialf  or 
three-quarters  of  a  mile  of  the  Menominee  River  at  the  Big  Quinnesec 
Falls,  but  only  a  few  of  its  apophyses  cross  the  river  into  Michigan.  It  is 
this  granite  which  Brooks  regarded  as  Huronian  in  age  (see  p.  61).  It 
undoubtedly  intrudes  the  Quinnesec  schists  and  is  younger  than  these;  but 
that  it  is  as  young  as  Brooks  supposed  is  doubtful,  since  none  of  its 
apophyses  intrude  the  Lower  Huronian  sediments.  It  is  to  this  complex  of 
acid  and  basic  schists,  cut  by  dikes,  that  the  name  Quinnesec  schists  is 
applied.  A  second  area  of  Quinnesec  schists  occurs  in  the  central  part  of 
the  west  end  of  the  trough.  Only  its  east  end  comes  within  the  limits  of 
the  map.  It  appears  as  a  narrow  wedge-shaped  area  widening  toward  the 
west.  It  is  surrounded  on  the  north,  east,  and  west  sides  by  the  Menominee 
sediments.  To  the  west  it  crosses  the  Menominee  River  into  Wisconsin, 
where  it  has  not  yet  been  studied  in  detail.  The  rocks  are  greenstone- 
scliists  and  ellipsoidal  greenstones,  cut  here  and  there  by  basic  dikes.     The 

130 


ARCHEAN,  QUINNESEC  SCHISTS.  131 

area  bordering  the  Menominee  River  to  the  south  of  the  trough  is  referred 
to  in  the  following  pages  'as  the  southern  area  of  Quinnesec  schists,  and 
that  within  the  west  portion  of  the  trough  as  the  western  area. 

SECTION  1.  QLUNNESEC  SCHISTS. 

RELATIONS   TO  OVERLYING  FORMATIONS. 

In  neither  the  southern  nor  the  western  areas  have  contacts  of  the 
Quinnesec  schists  with  the  sedimentary  rocks  of  the  Huronian  series  been 
seen.  There  is  no  positive  proof  that  the  green  schists  are  older  than  the 
Huronian  rocks.  There  can  be  little  doubt,  however,  that  the  schists  belong 
in  the  Archean.  They  have  all  the  complex  lithological  and  structural 
features  that  are  recognized  as  characteristic  of  typical  Archean  greenstone- 
schists  elsewhere.  They  are  mainly  volcanic  or  intrusive  rocks  which  have 
been  subjected  to  intense  metamorphism  and  which,  in  consequence  of  this, 
have  acquired  a  marked  schistosity.  No  ordinary  sediments  have  been 
discovered  among  them.  Moreover,  the  schists  are  in  every  respect 
identical  with  similar  scliists  in  the  Marquette  district  of  Michigan  that 
have  been  demonstrated  to  be  unconformably  beneath  the  Lower  Huronian 
sediments"  of  tliat  district,  and  they  are  also  identical  with  greenstone- 
schists  in  the  Vermilion  district  of  Minnesota  that  possess  similar  relations 
to  the  oldest  Huronian  sediments  of  that  district. 

Kxposui-es  of  the  two  series  are  found  in  closest  proximity  on  the 
Menominee  River  near  the  Fourfoot  Falls.  The  Chicago  and  Nortliwestern 
Railway  bridge  crossing  the  river  at  this  place  is  built  on  ledges  of  the 
schist.  Below  the  bridge  is  a  long  exposure  of  black  slate  belonging  to  the 
H  anbury  formation  of  the  Upper  Menominee.  The  schists  and  the  slates 
are  separated  by  a  distance  of  about  150  paces,  and  this  interval  is 
occupied  by  sand  and  glacial  drift  (see  also  p.  289). 

THE   SOUTHERN   AREA. 
DISTRIBUTION. 

The  southern  area  of  Quinnesec  schists  borders  the  south  side  of  the 
Menominee  trough.  Its  northern  boundary  extends  along  the  Menominee 
River  from  a  point  a  short  distance  below  the  mouth  of  Pine  Creek  to 
the  eastern  limit  of  the  area  mapped.  The  line  enters  Michigan  at  the 
south  town  line  of  T.  40  N.,  R.  31  W.,  runs  a  little  south  of  east  to  the 

«Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897,  pp.  152-168. 


132  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Big  Quinuesec  Falls,  where  it  crosses  to  the  Wisconsin  side  and  con- 
tinues its  course  iu  a  nearly  straight  line  to  the  Little  Quinnesec  Falls. 
Hei'e  it  recrosses  the  river  into  Michigan,  where  it  remains.  From  the 
Little  Quinuesec  Falls  it  rans  approximately  parallel  to  the  stream  as  far 
as  the  mouth  of  the  Stm-geon  River.  At  this  point  it  leaves  the  river,  runs 
nearl}'  southeast  to  the  southeast  coi'uer  of  T.  39  N.,  R.  28  W.,  aud  then  a 
little  south  of  east  to  the  southeast  corner  of  sec.  4,  T.  38  N.,  K  28  W., 
where  it  is  lost  beneath  a  covering  of  sand.  The  southern  boundar}"  of 
the  schists  has  not  been  definitely  determined.  It  is  somewhere  in  Wis- 
consin, a  considerable  distance  south  of  the  Menominee  River,  which  is 
practically  the  limit  of  the  area  discussed  in  this  report. 

TOPOGKAPHY. 

The  topography  of  the  southern  area  underlain  by  Quinnesec  schists 
is  rough  and  broken,  at  least  it  is  so  over  most  of  the  valley  of  the 
Menominee  River,  where  the  area  has  been  most  carefully  studied.  In  the 
bed  of  the  river,  where  the  channel  is  cut  through  the  schists,  are  great 
ledges  of  rocks  forming  rapids  and  falls,  and  along  its  banks  are  often 
craggy  precipices  and  shelving  rock  walls.  Three  noted  falls  exist  within 
that  portion  of  the  district  here  described.  These  are  the  Big  and  the 
Little  Quinnesec  Falls  and  Sturgeon  Falls  (PI.  X,  ^-1),  all  of  which  are 
over  the  harder  and  more  massive  ledges  of  the  schists  or  of  the  intru- 
sives  associated  with  them.  The  most  famous  rapids  are  the  Horserace 
Rapids  (PI.  XI,  A),  the  head  of  which  is  situated  a  few  hundred  yards 
below  the  bridge  of  the  Chicago,  Milwaukee  and  St.  Paul  Railway.  At 
this  place  the  river  dashes  through  a  narrow  rock-walled  gorge,  over  a 
rough  aud  rugged  channel  in  a  series  of  plunging  falls  and  seething  cal- 
drons. The  schists  here  have  been  greatly  metamorphosed  by  the  intrasion 
through  them  of  enormous  dikes  of  granite  and  porphyry.  These  harder 
portions  produce  the  falls  and  the  softer,  less  metamorphosed  portions 
between  the  intrusions  give  rise  to  the  caldrons.  Although  less  than 
half  a  mile  long,  the  Horserace  is  dreaded  by  tlie  lumberman  more  than' 
any  other  stretch  in  the  river,  since  here  are  formed  every  year  great 
jams  of  logs  that  are  extremely  expensive  to  break.  In  PI.  XI,  B,  is  shown 
the  rock-liound  channel  filled  with  logs.  Between  the  various  falls  and 
rapids  are  comparatively  long  stretches  of  quiet  water  (PI.  X,  B).  The 
general  character  of  the  stream  may  be  judged  fi-om  the  fact  that  the  fall 


U.   S.   GEOLOGICAL   SURVEY 


MONOGRAPH    XLVI       PL.    X 


A.     VIEW    FROM    BRINK   OF  STURGEON    FALLS,    LOOKING    DOWNSTREAM. 

The  barrier  rock  is  a  saussuritized  gabbro,  seen  to  the  left.     The  rocks  to  the  right,  limiting  the  basin  below  the  fails,  are  gabbros  and  schists 

derived  from  gabbros  and  diabases. 


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7)*.      MENOMINEE    RIVER   ABOVE  STURGEON    FALLS, 
One  of  the  quiet  basins  in  the  Quinnesec  schist  area  produced  by  the  backwater  above  the  falls. 


ARCHEAN,  QUINNESEC  SCHISTS.  133 

of  the  river  is  about  2G0  feet  in  the  20  miles  of  its  course  betweeu  the  point 
west  of  Iron  Mountain,  where  it  enters  the  southern  area  of  schists,  to  the 
point  where  it  crosses  the  east  range  Une  of  T.  38  N.,  R.  29  W.,  neai-  the 
southeast  limit  of  the  map.  When  it  is  realized  that  only  about  14  miles 
of  this  course  is  in  the  schists,  and  that  in  this  distance  nearly  all  the  fall  is 
made,  some  idea  may  be  gained  as  to  the  roughness  of  the  stream.  The 
fact  that  more  than  half  of  this  fall  is  made  at  Sturgeon  Falls  and  at  the 
Big  and  Little  Quiunesec  Falls,  affords  abundant  opportunity  for  the 
development  of  immense  power  at  these  localities  when  economic  condi- 
tions for  its  utilization  are  more  favorable  than  they  are  at  present.  At 
the  Little  Quimiesec  Falls,  where  about  10,000  horsepower  is  available  for 
use,  there  is  now  a  paper  mill  which  employs  less  than  half  of  this  power, 
and  at  the  Big  Quinnesec  Falls  is  an  air-compressor  plant.  The  greater 
portion  of  the  power  of  the  stream  in  this  area  is,  however,  not  used  for 
any  purpose. 

Away  from  the  ri\er  the  country  underlain  by  the  schists  is  very 
rough,  though  lofty  eminences  and  deep  valleys  are  not  noticeable.  The 
topography  is  made  up  of  many  ridges  and  elongated  hills  having  steep 
slopes  covered  with  thin  layers  of  soil,  or  precipitous  sides  of  bare  rock. 
On  the  tops  of  the  hills  bare  flat  ledges  are  met  with,  here  and  there  cov- 
ered with  patches  of  soil  an  inch  or  so  thick. 

On  the  Michigan  side  of  the  river  a  thick  mantle  of  sand  and  glacial 
drift  lies  ujjon  the  schists  and  obliterates  their  characteristic  topography, 
but  very  close  to  the  river  bank,  where  recent  erosion  has  removed  the 
sand,  and  along  the  Wisconsin  shore,  for  a  few  miles  from  the  bank,  the 
rugged  nature  of  their  surface  is  well  shown. 

COMPOSITION    AND    STRUCTURE    OF   THE    ROCK   SERIES. 

The  Quinnesec  schists  of  the  southern  area  consist  mainly  of  schistose 
basic  and  acid  igneous  rocks  and  a  few  basic  tuff's."     The  former  comprise 

"Althougli  tuffs  are  only  rarely  found  in  the  area  included  in  this  study,  they  are  by  no  means 
rare  in  the  extension  of  the  schist  area  south  of  the  Menominee  River.  About  midway  between  this 
river  south  of  Norway  and  the  "Soo"  Railroad  in  Wisconsin,  there  are  great  hillocks  and  bare  bluffs 
that  are  composed  exclusively  of  coarse  greenstone  conglomerates  like  those  so  abundant  in  the 
northern  Archean  complex  in  the  Marquette  district,  and  interlaminated  beds  of  fairly  well-banded 
greenstone  tuffs.  The  area  has  not  been  studied,  Ijut  from  the  great  magnitude  of  these  deposits  at 
the  locality  referred  to,  it  appears  probaVile  that  volcanic  fragmentals  play  a  much  greater  part  in  the 
constitution  of  the  (^uinnesec-schist  complex  than  would  be  inferred  from  studies  confined  to  that 
portion  of  the  schist  area  in  the  neighborhood  of  the  Menominee  River. 


134  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

chloi-ite-schists,  ampliibolites,  schistose  diabases,  schistose  diorites,  and 
schistose  gabbros.  AVith  these  are  large,  ahnost  massive  la3^ers  of  gabbro 
aud  diorite  that  ai-e  supposed  to  be  interbedded  sills  or  flows,  and  dikes  of 
gabbro,  diorite,  diabase,  and  granite.  The  basic  schists  constitute  by  far 
the  greater  part  of  the  schists  of  the  area,  but  in  the  vicinit}'  of  the  Horse- 
race Eapids  and  of  the  the  Big  Quinnesec  Falls,  the  basic  rocks  are  asso- 
ciated with  large  quantities  of  acid  ones.  The  acid  rocks  are  in  some 
places  nearly  massive  granites,  in  other  places  they  are  gneisses,  and  in 
still  other  places  they  are  finely  banded  and  schistose  rocks  like  the  Saxon 
granulites.  The  last-named  rocks  occur  in  bands  of  different  widths,  nearly 
always  striking  conformably  with  the  strike  of  the  foliation  of  the  basic 
schists  with  which  tliev  are  associated.  The  schistosity  of  the  bands  is 
pai-allel  to  the  schistosit}^  of  the  adjoining  schists,  irrespective  of  the  direc- 
tion of  the  band  itself  Although  rather  irregular  in  their  distribution, 
the  different  schists  may  be  observed  to  occur  in  more  or  less  well-defined 
belts  extending  for  comparatively  short  distances  in  approximately  straight 
lines.  These  belts  strike  a  little  north  of  west  at  the  Sturgeon  Falls,  a 
little  south  of  west  at  the  Little  Quinnesec  Falls,  and  about  northwest  at  the 
Big  Quinnesec  Falls.  Tlieir  schistosity  strikes  approximately  parallel 
to  the  trend  of  the  belts,  but  not  ahvays  exacth'  so.  The  dip  varies  slightly 
in  different  ledges,  but  is  never  far  from  perpendicular.  On  the  northern 
and  eastern  peripheries  of  the  granite  boss  in  Wisconsin  the  foliation  of  the 
schists  is  very  well  developed.  Here  the  schistosity  is  nearl)^  parallel  to 
the  contacts  with  the  granite,  changing  with  the  trend  of  this  boundary 
and  following  in  a  general  way  its  sinuosities.  Tliis  fact  suggests  that  the 
schistosity  of  these  rocks  is  due  to  pressure  and  that  its  direction  is  deter- 
mined by  the  directions  of  the  lines  along  which  the  stresses  acted,  i.  e., 
along  lines  at  right  angles  to  the  boundary  of  the  granite  boss. 

LITHOLOGY. 

There  is  very  little  to  add  to  the  account  of  the  lithological  features  of 
the  Quinnesec  schists  given  by  Williams"  in  his  bulletin  on  the  Marquette 
and  Menominee  greenstone-schists.  In  this  report  the  author  presents 
excellent  descriptions  of  all  the  various  forms  of  schists  met  with  along,  the 

ff  Williams,  George  Huntington,  The  greenstone  schist  areas  of  the  Menominee  and  Marquette 
regions  of  Michigan,  with  an  introduction  by  Eoland  Duer  IrWng:  Bull.  U.  S.  Geol.  Survey  No.  62. 
1890. 


ARCHEAN,  QUINNESEC  SCHISTS.  135 

Menominee  River  and  describes  in  detail  the  character  of  the  intrusion 
traversing  them.  There  seems  to  be  no  need  of  duplicating  these  descrip- 
tions in  the  present  volume.  In  the  following  pages  a  brief  summary  of 
Williams's  discussion  will,  however,  be  given,  and  a  few  additions  will  be 
made  to  his  descriptions  in  order  that  the  great  similarity  between  the 
Arcliean  in  this  and  other  districts  may  be  clearly  perceived,  and  that  the 
great  contrast  always  existing  between  the  Archean  and  the  Huroniau 
rocks  of  the  Lake  Superior  region  may  again  be  emphasized. 

For  purposes  of  description  the  Quinnesec  schists  may  be  divided  into 
greenstone-schists,  chlorite-schists,  amphibolites,  gneisses,  and  sericite-schists. 
The  massive  rocks  associated  with  them  may  be  classed  as  greenstones  and 
granite.  The  greenstones  include  gabbros,  diorites,  dialjases  and  basalts; 
the  granites  include  granite  and  granite-porphyry.  Because  of  the  close 
genetic  relationship  existing  between  the  greenstones  and  the  greenstone- 
schists  on  the  one  hand  and  between  the  granites  and  the  acid  schists  on  the 
other  hand,  the  former  will  be  described  together,  as  will  also  be  the  latter. 

«iBEE>'STO>E-Si;HISTS  AXD  ASSOCIATED  tiREENST(^IVES. 

The  term  greenstone-schists  is  applied  to  those  basic  schists  which 
show  clearly  by  their  composition  and  structure  that  they  were  derived  from 
basic  igneous  rocks.  They  grade  on  the  one  side  into  massive  gabbros, 
diorites,  diabases,  basalts,  and  basic  tuffs,  and  on  tlie  other  side  into  the 
chlorite-schists  and  amphibolites.  Specifically  they  might  be  termed  gabbro- 
gneisses,  diorite-gneisses,  etc.,  but  their  present  mineralogical  and  chemical 
composition  is  so  different  from  that  of  the  corresponding  massive  rocks  that 
it  is  thought  best  to  refer  to  them  under  the  generic  term  greenstone-schists. 
The  term  is  a  convenient  one,  partly  because  it  is  so  comjjrehensive,  and 
partly  because  some  such  term  is  absolutely  necessary  to  the  prosecution  of 
field  work  in  regions  of  ancient  schist  complexes.  The  term  comprehends 
all  dark-colored  schistose  feldspathic  rocks  derived  from  massive  igneous 
rocks  and  their  tuffs.  In  the  Menominee  district  the  greenstone-schists 
comprise  schistose  gabbros,  diabases,  diorites,  basalts,  diabase  tuffs,  and 
basalt  tuffs.  They  vary  in  color  from  greenish  gray  to  greenish  black,  in 
texture  from  coarse  grained  to  aphanitic,  and  in  structure  from  almost 
massive  to  perfectly  schistose.  The  more  massive  phases  are  sometimes 
poikilitic.  The  finer-grained  rocks  are  usually  more  schistose  than  the 
coarse-grained  ones,  though  not  always  so.     The  most  perfect  schistosity, 


136  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

amounting  almost  to  perfect  fibrosity,  is  met  with  only  in  the  aphanitic 
phases.  The  rock  of  nearly  every  exposure,  or  at  least  of  every  group  of 
exposures,  possesses  a  characteristic  appearance  which  differs  from  that  of 
cori-esponding  rocks  of  other  ledges,  so  that  a  detailed  description  of  the 
macroscopic  features  of  all  the  different  greenstone-schists  of  the  district 
would  be  nothing  more  or  less  than  a  description  of  individual  specimens. 
The  same  statement  applies  to  the  description  of  the  massive  greenstones. 
A  detailed  description  of  this  kind  does  not  seem  necessary  in  this  place, 
especially  since  Williams  has  so  well  described  nearly  all  the  several  phases 
of  the  greenstones  and  their  schists  in  the  bulletin  referred  to  above.  Only 
the  principal  and  predominating  types  of  the  schists  will  be  described  in 
the  following  pages,  the  unusual  types  being  referred  to  only  in  the  descrip- 
tions of  interesting  localities. 

COARSE-GRAINED    VARIETIES. 

The  material  of  the  coarse-grained  schists,  which  may  represent  dikes, 
or  flows  of  coarse  lavas  in  a  series  of  finer-grained  lavas,  differs  very  little 
from  the  material  of  the  coarse-grained,  massive  greenstone  dikes  cutting 
through  the  schist  series.  Most  of  these  rocks  are  light-gray  diabasic 
aggregates  of  a  white  feldspathic  mineral  and  a  greenish-gray  hornblendic 
one,  with  occasionally  here  and  there  an  irregular  grain  of  magnetite  or 
ilmenite.  Others  are  darker  in  color  and  greener  in  tinge.  In  these  the 
hornblendic  mineral  predominates  and  the  feldspar  is  often  epidotized.  In 
most  specimens  the  feldspar  is  in  diabasic  forms,  in  others  it  is  in  the  irreg- 
ular grains  characteristic  of  gabbro,  and  in  still  others  it  is  in  rounded 
phenocrysts.  Near  slickensided  surfaces  the  characteristic  gabbro  or  dia- 
basic structure  disappears,  and  the  rock  becomes  a  typical  chlorite-schist  or 
amphibole-schist. 

Gahhros  and  their  derived  schists. — The  barrier  rock  of  Sturgeon  Falls 
(see  PI.  X,  A)  is  an  excellent  example  of  one  of  the  most  massive  phases 
of  the  coarse-grained  rocks.  It  is  not  known  whether  it  is  a  dike  or  an 
immense  flow.  It  exhibits  many  lithological  features  of  the  massive  dikes, 
and  at  the  same  time  it  possesses  phases  that  are  identical  in  character  with 
those  of  many  of  the  coarser-grained  schists."  The  most  massive  phase  of 
the  rock  is  light  gray  in  color.     On  a  fresh  fracture  it  is  mottled  in  white 

«Cf.  Williams,  op.  cit.,  p.  68. 


ARCHEAN,  QQINNESEC  SCHISTS.  137 

and  dark-greenish  gray,  the  consequence  of  the  presence  of  a  greenish- 
white  feldspar  and  a  brownish,  lustrous  amphiboloid.  The  texture  is 
moderately  fine,  but  is  subject  to  sudden  local  variations  which  develop 
comparatively  coarse-grained  patches  in  the  main  mass.  Under  the  micro- 
scope the  rock  is  discovered  to  be  a  gabbro  in  which  there  still  remain 
renmants  of  colorless  diallage,  but  in  which  the  plagioclase  has  been  almost 
wholly  altered  to  a  gray  and  opaque  saussurite.  Most  of  the  original 
diallage  has  been  changed  to  a  compact  brown  amphibole,  which,  togetlier 
with  calcite,  albite,  chlorite,  and  quartz,  are  the  principal  secondary  products 
present.  All  specimens  exhibit  the  action  of  dynamic  forces  that  have 
more  or  less  profoundly  affected  the  different  constituents. 

The  rock  seems  in  places  to  have  been  crushed  and  a  mosaic  of  the  component 
minerals  to  have  been  formed.  Hornblende,  generally  colorless,  is  unusually  abun- 
dant. Colorless  chlorite  and  zoisite  are  also  developed,  and  all  are  mixed  indiscrim- 
inately. In  one  part  of  the  section  a  vein  is  seen  to  traverse  the  rock.  This  is  tilled 
with  limpid  quartz  in  long-,  wedge-shaped  areas,  which  extend  from  one  side  of  the 
small  fissure  to  the  other.  This  quartz  is  traversed  by  long,  colorless  fibers  of  the 
greatest  delicacy,  and  it  also  contains  a  good  deal  of  the  colorless  chlorite,  both  in  solid 
masses  and  in  those  peculiar  vermicular  groups  to  which  Volger  has  given  the  name 
helminth.  These  curious  groups,  which  resemble  piles  of  little  coins,  are  sometimes 
straight,  sometimes  curved.  They  are  so  minute  as  to  be  visible  only  with  a  high 
magnifying  power." 

In  the  more  schistose  phases  of  the  rock  the  constituent  minerals,  while 
the  same  as  those  in  its  less  schistose  phases,  have  suffered  much  greater 
changes. 

The  feldspar  is  remarkably  fresh  and  its  twinning  lamellse  are  quite  distinct,  but 
it  is  everywhere  crushed,  broken,  and  faulted.  The  crystals  are  often  plainly  seen  to 
be  separated  into  a  number  of  fragments  which  are  removed  a  considerable  distance 
from  one  another.  Frequentlj^  a  fine-grained  mosaic  has  been  formed  by  the  crush- 
ing of  the  largei-  feldspar  crystals.  In  other  cases  *  *  *  the  feldspar  is  not  so 
much  broken,  but  it  is  altered  ai-ound  its  edge  to  an  opaque  gray  saussuritic  mass, 
while  its  interior  is  hardly  changed.  *  *  *  The  diallage  is  more  altered  than  in 
the  rocks  last  described.  *  *  *  The  crystals  are  very  much  bent  and  twisted 
and  frequently  so  changed  to  the  light-colored  chlorite  that  only  a  few  minute 
remnants  of  the  brightly  polarizing  mineral  remain  in  this  nearly  isotropic  l)ase. 
*  *  *  Fibrous  hornblende  now  becomes  more  abundant  than  the  compact,  and 
leucoxene  patches  are  seen  at  intervals.* 


a  Williams,  op.  cit.,  p.  71.  ''Ibid.,  p.  72. 


138 


THE   MENOMINEE  IRON-BEAKING  DISTRICT. 


The  compact  massive  or  slightly  schistose  rock  passes  gradually  into 
softer,  more  schistose,  ones,  that  have  lost  all  traces  of  their  original  structure 
and  of  their  original  mineral  composition  as  well.  The  schists  are  now 
composed  of  broken  pieces  of  feldspar  which  has  been  almost  comjjletely 
changed — 

to  an  aggregate  of  calcite  and  minute  brightly  polarizing  needles  or  plates  of  a 
colorless  micaceous  mineral  (probably  sericite)  along  with  occasional  areas  of 
secondary  quartz.  What  was  once  the  pyroxene  or  hornblende  is  now  a  colorless  or 
extremely  pale-green,  scalj'  mineral,  which  an  examination  shows  to  be  chlorite.. " 

The  most  schistose  phases  of  the  rock  are  examples  of  fissile,  silky, 
chloritic  schists,  composed  of  a  fine-grained  schistose  aggregate  of  colorless 
chlorite,  quartz,  and  calcite. 

These  rocks  are  schists,  indeed,  of  the  most  characteristic  type,  but  in  the  light 
of  their  field  relations,  and  still  more  from  the  evidence  which  a  microscopical  studj^ 
of  the  whole  series  has  afforded,  it  is  evident  that  they  represent  the  most  altered 
form  of  the  massive  gabbro,  between  two  areas  of  which  they  are  included.  * 

The  chemical  changes  undergone  by  the  gabbro  in  its  transition  to  a. 
schist  are  shown  by  the  following  three  analyses  made  for  Dr.  Williams  by 
Dr.  R  B.  Riggs: 

Analyses  of  gahhro  and  schist  from  Sturgeon  Falls. 


SiO^ 

AlA 

FeA 

FeO 

CaO 

MgO 

Na,0 

K,0 

H^O 

CO2 

Total 


I. 


51.46 

14.35 

3.90 

5.28 

9.08 

9.54 

2.92 

.24 

3.30 

.20 


100. 27 


II. 


38.05 

24.  73 

5.65 

6.08 

1.25 

11.58 

2.54 

1.94 

7.53 

.93 


100.28 


III. 


45.70 
16.53 
4.63 
3.89 
4.28 
9.57 
.55 
3.82 
4.70 
5.95 


99.62 


Rock  powder  dried  at  105°  C. 

I.  Freshest  gabbro  from  barrier  rock  of  Sturgeon  Falls, 
II.  Schistose  galibro  from  south  side  of  I. 
III.  Silvery  chlorite-schist  from  band  between  two  bands  of  saussuritized  gabbro. 


"Williams,  op.  cit,  p.  73. 


nbid.,  p.  75. 


ARCJHEAN,  QUINNESEC  SCHISTS.  139 

The  most  marked  variations  noted  in  the  composition  of  the  three 
rocks  is  with  reference  to  the  lime,  alumina,  soda,  potash,  and  carbon 
dioxide.  Williams  explains  the  fact  that  the  intermediate  rock  (II)  differs 
more  from  the  original  type  (I)  than  does  the  most  schistose  phase  (III) 
by  supposing  that  the  processes  of  alteration  have  been  different  in  the 
two  altered  phases.  In  the  first  case  the  main  i)roduct  of  the  alteration 
lias  been  chlorite;  in  the  second  case  it  is  sericite  and  calcite.  It  is 
difficult  to  conceive  a  process  which,  acting  upon  two  portions  of  the 
same  rock  close  together,  will  cause  chloritization  in  one  part  and  sericiti- 
zation  in  the  other.  The  production  of  sericite  in  a  rock  of  the  composition 
of  a  gabbro  necessitates  the  addition  of  potash  and  alumina  from  some 
extraneous  source,  through  the  transporting  agency  of  solutions.  It  is 
very  difficult  to  understand  how  such  solutions  might  be  confined  to  a 
certain  definite  band  in  an  altering  basic  rock  and  be  practically  excluded 
from  other  portions  of  the  same  rock.  It  is  more  probaljle  that  the  three 
rocks  whose  analyses  are  given  above  originally  possessed  different  com- 
positions, and  that  this  accounts  for  their  differences  in  composition  at 
present. 

Diabases  and  their  derived  schists. — The  coarse  diabases  and  their  derived 
schists  are  in  all  essential  respects,  except  structure,  like  the  gabbro  and 
the  gabbro-schists. 

Diorites  and  their  derived  schists. — The  diorites  and  the  schists  derived 
from  them  are  slightly  different  from  the  gabbros  and  their  associated  schists, 
but  the  processes  which  changed  the  massive  rocks  into  schistose  phases 
were  practically  the  same  in  both  cases.  The  rock  forming  the  high  bluff 
skirting  the  east  side  of  the  river  below  the  Little  Quinnesec  Falls  is  the  best 
example  of  the  massive  diorite  met  with  in  the  district.  It  is  described  by 
Williams  as  being  in  all  probability  a  great  dike.  Though  for  the  most  part 
quite  massive,  the  rock  presents  frequent  and  instructive  evidence  of  the 
effect  of  great  pressure  upon  it. 

It  is  seamed  and  gashed,  broken  and  torn,  and  contains  schistose  bands  of  varying 
width.  Since  the  continuity  of  these  bands  with  the  massive  rock  is  established, 
their  study  is  calculated  to  throw  light  on  the  subject  of  dynamical  metaraorphism. 

Major  Brooks  designated  the  rock  which  composes  this  ridge  as  a  "massive 
gabbro,"  and  correlated  it  with  the  above-described  saussurite-gabbro  of  Sturgeon 
Falls.  My  studies  have,  however,  failed  to  disclose  in  this  rock  any  trace  of  pyroxene. 
In  addition  to  its  feldspathic  constituent,  which  is  generally  altered  to  saussurite,  it 
contains  in  abundance  that  peculiar  pale-green  and  more  or  less  librous  variety  of 


140  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

hornblende  which  is  quite  universally  conceded  to  be  of  secondary  origin.  What  the 
primar}'  form  of  all  this  green  hornblende  was,  it  is  now  impossible  to  ascertain  with 
certainty.  It  is  of  a  kind  well  known  to  originate  from  the  alteration  of  pyroxene. 
The  rock  as  a  whole  also  bears  decidedly  the  character  of  a  diabase  or  pyroxene  rock; 
and  yet,  not  a  trace  of  pyroxene  has  been  discovered  in  any  of  the  Menominee  River 
greenstones,  if  we  except  the  light-colored  diallage  of  the  Sturgeon  Falls  gabbro. 
Whenever  the  pale-green  hornblende  can  be  traced  back  to  an  original  form,  it  is 
seen  to  be  derived  from  a  compact  brown  or  basaltic  hornblende. 

******* 
It  is,  of  course,  impossible  to  prove  that  some  of  the  secondary  fibrous  hornblende 
has  not  been  derived  from  pyroxene.  Indeed,  it  seems  very  probable  that  both  augite 
and  compact  brown  hornblende  may  have  existed  side  by  side  as  original  constituents 
of  the  rock,  and  that  both  finally  succumbed  to  the  same  process  of  alteration,  although 
the  hornblende  resisted  this  much  longer  than  the  augite.  *  *  *  Inasmuch, 
however,  as  the  rocks  here  under  discussion  afford  no  trace  of  pyroxene,  it  hardly 
seems  justifiable  to  call  them  anything  but  diorite." 

Some  of  the  pliases  of  the  rock  are  porphyritic.  These  contain  large 
crystals  of  saussuritized  feldspar  in  a  matrix  composed  wholly  of  hornblende 
in  compact,  brown  and  green,  or  colorless  grains,  and  in  light-green  fibers, 
in  which  are  embedded  small  laths  of  plagioclase.  The  hornblende  by 
alteration  passes  into  chlorite  and  tremolite. 

The  schists  derived  from  the  diorite  are  largely  chlorite-schists.  They 
present  no  peculiar  features  distinguishing  them  from  the  schists  derived 
from  the  gabbro,  except  in  those  phases  where  the  structure  of  the  original 
rock  is  still  retained.  At  one  place  toward  the  west  end  of  the  diorite  ridge 
a  well-marked  band  of  schist  traverses  the  massive  rock.     The  latter  is — 

composed  of  stout  rectangular  feldspars,  with  a  somewhat  rounded  outline,  and 
internally  changed  to  saussurite,  though  their  periphery  is  mostly  clear.  Between 
these  are  the  remains  of  former  hornblende  (possibly  pyroxene)  individuals  now 
represented  only  by  amphibole  fibers  and  chlorite.  Beautiful  skeleton  forms  of 
leucoxene,  composed  of  three  sets  of  parallel  bands  reproducing  the  rhombohedral 
parting  of  the  original  ilmeaite,  are  abundant.* 

The  rock  of  the  schist  baud  is  much  more  altered.  Its  feldspar  is 
mostly  changed  to  calcite,  and  the  hornblende  to  chlorite.  The  original 
structure  has  wholly  disappeared,  and  there  is  now  a  fine  mosaic  of  quartz 
and  secondary  albite  between  the  calcite  and  chlorite  masses.  The  same 
skeleton  forms  of  leucoxene  remain,  however,    and    "  there  is  no  doubt 


o  Williams,  op.  cit.,  pp.  77-78.  bJbid.,  p.  83. 


ARCHEAN,  QUINNESEC  SCHISTS.  141 

that  the  two  specimens  represent  the  same  rock  in  different  stages  of 
alteration,  the   more   changed  form   liaving  become  decidedly  schistose." " 

FINE-GRAINED    VARIETIES. 

The  finer-grained  greenstones  and  greenstone-schists  were  originally 
diabases,  basalts,  and  basic  tnffs.  In  composition  they  are  similar  to  the 
coarser-grained  varieties  described.  Their  structure  is  less  well  defined, 
and  in  some  cases  the  original  rock  appears  to  have  been  essentially  a  glass. 
One  of  the  best  preserved  of  the  fine-grained  rocks  is  that  on  the  Michigan 
side  of  the  Little  Quinnesec  Falls.  It  is  a  massive,  dark-green  rock  which, 
according  to  Williams — 

was  originally  a  diabase,  although  its  present  constituents  are  for  the  most  part 
secondary.  The  shapes  of  the  original  minerals  are  indistinctly  outlined,  and  so  the 
structure  of  the  rock  is  preserved.  There  is  now  present  a  pale-green  hornblende, 
probably  secondary  to  pyroxene,  although  no  traces  of  this  mineral  are  preserved; 
epidote,  chlorite,  saussurite,  and  leucoxene  in  zones  around  the  titanic  iron.  The 
feldspar  has  rarely  changed  to  the  opaque,  gray  saussurite,  but  is  replaced  for  the 
most  part  by  a  mass  of  shai-ply  defined  epidote  crystals.  Where  the  feldspar  and 
hornblende  have  jointly  contributed  to  the  formation  of  secondary  products,  we 
have  the  chlorite-epidote  aggregate  as  a  result.  A  little  secondary  quartz  is  also 
observable.'' 

These  massive  or  almost  massive  rocks,  as  has  been  said,  arrade  in 
many  places  into  schists.  Where  they  do  not  actually  pass  into  schistose 
phases  they  are  often  associated  with  basic  schists  in  which  traces  of  the 
original  structure  of  eruptives  can  be  detected  or  which  can  be  traced  into 
rocks  exhibiting  this  structure.  In  other  cases,  as  stated  by  Wadsworth'^ 
in  connection  with  the  discussion  of  the  origin  of  these  rocks  at  the  Little 
and  the  Big  Quinnesec  Falls,  the  basic  schists  may  have  been  derived 
from  volcanic  tuffs  or,  as  Wadsworth  calls  them,  porodites.  The  predomi- 
nant rock  on  the  Michigan  side  of  the  lower  falls,  for  instance,  is  jolainly 
conglomeratic.  It  is  either  an  old  eruptive  ash  or  an  agglomerate.  "Of 
the  fragmental  and  conglomeratic  nature  of  the  rock,"  Wadsworth  declares, 
"no  one  can  possibly  doubt  after  studying  it  on  the  Michigan  side,  below 
the  falls,  and  then  tracing  it  back  into  the  finer  grained  and  more  compact 
part  near  the  bridge." 


"Williams,  op.  cit.,  p.  83. 
6 Ibid.,  p.  94. 

c  Wadsworth,  M.  E.,   Report  of  State  Board  of  Geological  Survey  for  1891  and  1892,  Lansing, 
1890,  p.  125. 


142  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Origin  of  the  schistosity. — The  least-altered  phases  of  the  fine-grained 
greenstones  are  characterized  by  a  rhomboidal  parting.  As  the  rocks 
depart  more  and  more  from  their  original  character  the  rhombs  produced 
by  the  parting  become  more  and  more  elongated  nntil  finally  their  sides 
are  approximately  parallel  and  a  well-developed  schistosity  results.  At  the 
same  time  the  original  components  of  the  rock  mass  undergo  change.  In 
many  of  the  less-altered  schists  that  have  been  derived  from  massive 
eruptives  the  structure  of  the  originals  can  still  be  recognized,  though  their 
mineral  composition  can  only  be  surmised,  since  they  consi.st  of  secondary 
products  exclusively. 

Basic  lavas  and  their  derived  schists. — In  the  field,  dark-  and  light- 
colored  schists  are  readily  distinguished,  and  both  are  closely  associated 
with  nearly  massive  phases.  On  the  east  side  of  the  basin,  below  the  Little 
Quinnesec  Falls,  the  dark  schists  are  so  intimately  associated  with  massive 
greenstones  that  there  can  be  little  doubt  as  to  the  original  identity  of  the 
two.  In  the  hand  specimen  the  least  schistose  rock  is  a  compact,  aphanitic 
mass  of  a  dark -green  color. 

Under  the  microscope  the  original  diabasic  nature  of  the  rock  is  at  once 
apparent,  although  the  extensive  mineralogioal  changes  which  have  gone  on  have 
greatly  obscured  its  former  structure.  The  components  now  present  are  almost 
wholly  secondary.  These  are  hornblende,  chlorite  containing  epidote.  quartz,  and 
leucoxene.  Ilmenite  and  occasional  traces  of  feldspar  are  the  only  original  constit- 
uents which  remain.  Still,  the  disposition  of  the  secondary'  minerals  is  such  as  to 
outline  a  diabasic  or  ophitic  structure  often  with  great  distinctness.  The  feldspar  is 
rarely  well  preserved;  but  a  narrow  zone  of  the  unaltered  substance  of  this  mineral 
often  outlines  a  stoutly  lath-shaped  crystal,  even  when  its  interior  is  wholly  changed 
to  an  aggregate  of  quartz,  chlorite,  and  epidote.  The  hornblende  has  a  curious 
appearance.  Its  crystals  are  brownish  and  nonpleochroic  with  a  somewhat  granu- 
lated surface,  so  that  it  externally  resembles  diallage.  Its  cleavage  and  optical 
properties  prove  it  to  be  undoubtedly  hornblende,  although  this  superficial  likeness 
to  diallage  is  so  strong  as  to  almost  compel  the  conviction  that  it  has  originated  by 
paramorphism  from  a  pyroxene;  This  brown  hornblende  is  seen  with  a  high  power 
to  be  gradually  changing  to  a  green  variety,  in  which  a  pleochroism  for  the  first 
time  becomes  apparent.  This  also  frequently  passes  over  into  a  fibrous  hornblende. 
The  chlorite-epidote  aggregate  in  these  rocks  is  very  finely  developed.  The  chlorite 
is  of  an  emerald-green  color  and  distinctly  pleochroic.  It  appears  between  cro.ssed 
nicols  as  isotropic  or  polarizes  with  a  maroon  tint.  The  epidote  is  in  sharp, 
light-yellow  crystals,  with  the  characteristic  shape  and  optical  properties  of  this 
species.     *     *     *     This   chlorite-epidote  aggregate   covers   considerable  areas  and 


ARCHEAN,  QUINNESEC  SCHISTS. 


143 


occupies  the  place  of  both  the  feldspathic  and  the  pyroxenic  constituents.  In  addi- 
tion to  the  minerals  already  named,  ilmenite  with  its  leucoxene  border,  pyrite,  and 
secondary  quartz  are  quite  abundant  in  these  rocks.  " 

Through  this  rock  passes  a  schistose  band  so  intimately  related  to  the 
massive  rock  in  both  sides  of  it  that  there  can  not  be  the  least  doubt  as  to 
the  continuity  of  the  two.  The  hand  specimen  taken  from  the  band  is 
decidedly  schistose. 

Under  the  microscope  it  shows  the  effects  of  mechanical  crushing  and  attendant 
mineralogical  changes  with  great  distinctness.  The  whole  rock,  with  the  exception 
of  certain  remains  of  the  larger  feldspar  crystals,  has  been  reduced  to  a  fine-grained 
mass,  showing  an  aggregate  polarization.  Light-green  chlorite  has  been  largely 
developed  and  has  completely  replaced  all  the  bisiiicate  elements.  The  parallel 
arrangement  of  the  scales  of  this  mineral  is  what  produces  the  schistose  structure.* 

Tlie  chlorite  together  with  clear  grains  of  quartz  and  probably  of 
unstriated  feldspar  are  embedded  in  a  quartz-albite  mosaic.  Calcite  is  also 
abundant  as  little  nests  in  the  mosaic,  and  rutile  either  in  stout  yellow 
grains,  or  in  minute  sharp  crystals  traverse  it  in  long  sinuous  lines.  This 
rutile  represents  the  ilmenite  of  the  original  rock. 

The  mechanical  action  which  produced  this  schistose  band  has  therefore  resulted 
in  the  ci-ushing  of  the  rock,  and  the  almost  total  disappearance  of  all  of  the  original 
components.  The  comparatively  slight  change  in  the  chemical  composition  of  the 
rock  as  a  whole  may  be  seen  from  the  two  following  analyses  *  *  *  made  by 
Mr.  R.  B.  Riggs: 

Analyses  of  greenstone  from  Little  Quinnesec  Falls. 


I. 

II. 

I. 

II. 

SiO 

43.80 

16.08 

9.47 

10.50 

7.81 

6.54 

44.49 
16.37 
5.07 
5.50 
7.94 
7.50 

Na.p 

1.96 
0.34 
3.99 
0.08 

2  .59 

AI2O3 

K.fl 

0.56 

Fe^O., 

HjO 

4.99 

FeO                                  

CO.,     . 

5  38 

Total 

CaO                  .                

100.  57 

100.  39 

MkO 

TiOj  not  determined.     Powder  dried  at  105°  C. 
1.  Dark,  massive  greenstone,  Lower  [Little]  Quinnesec  Falls. 
II.  Dark,  schistose  greenstone,  forming  a  band  in  the  last. 


"Williams,  op.  cit.,  p.  90. 


''Ibid.,  p.  90. 


144  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  changes  here  are  at  once  seen  to  be  due  (1)  to  the  total  removal  of  the  iron 
ores  (losy  of  iron);  (2)  to  the  production  of  carbonates  (gain  of  CO^,  carbonatization) ; 
and  (3)  to  the  increase  in  the  amount  of  chlorite  (increase  of  tl.,0,  hydration)." 

These  darker  schists  pass  into  hghter  ones  that  are  more  typical  chlorite- 
schists,  composed  of  extremely  pale  chlorite  and  quartz  grains,  with  a 
little  calcite  and  occasional  sericite  shreds,  and  numerous  minute  sharp 
crystals  of  rutile.  Whether  these  lighter  schists  are  actually  phases  of  the 
darker  ones,  or  whether  the  two  are  schistose  phases  of  rocks  that  were 
originally  different,  can  not  now  be  told,  since  the  true  nature  of  the  con- 
tact between  them  has  been  obliterated  by  the  changes  through  which  the 
rocks  on  both  sides  of  it  have  passed.  Even  if  the  latter  be  the  case  the 
two  originals  were  not  very  different,  both  in  all  probability  being  basic 
lavas  or  tuff  beds. 

Basic  tuffs  and  their  derived  schists. — The  schists  derived  from  tuffs 
generally  exhibit  their  origin  in  their  structure  when  this  has  not  been 
completely  destroyed.  Usually,  however,  the  tufifaceous  structure  disap- 
pears so  rapidly  with  the  assumption  of  schistosity  that  nothing  remains 
to  distinguish  the  schists  derived  from  tuffs  from  those  derived  from  fine- 
grained  eruptives. 

In  a  few  instances  sections  made  from  the  schists  at  the  Little  Quln- 
nesec  Falls  possess  characteristics  that  point  to  a  tuflaceous  origin.  In 
natural  light  tliese  sections  show  irregular  granular  areas  and  black  dots  in 
a  colorless,  transparent,  almost  amorphous  matrix.  Between  crossed  nicols 
plagioclase,  saussurite,  kaolin,  calcite,  colorless  or  light-green  chlorite,  and 
bleached  hornblende  are  noticeable.  The  plagioclase  is  largely  altered 
into  chlorite,  saussurite,  and  kaolin.  The  greater  portion  of  the  mineral  is 
often  fresh  enough  ti)  exhibit  clearly  its  twinning  striations,  though  not 
fresh  enough  to  yield  accurate  measurements  of  extinction  angles.  This 
feldspar  occurs  in  lath-shaped  cr5^stals,  in  rounded  and  irregular-shaped 
grains,  in  sharji-edged  fragments,  and  in  some  instances  it  appears  as 
though  it  were  a  secondary  deposit  filling  triangular  spaces  between  the 
other  components.  Some  of  the  crystals  are  fairly  well  formed,  others  are 
broken,  and  still  others  are  castellated  at  their  ends.  A  large  number  of 
skeleton  crystals  are  also  noticed  scattered  through  the  matrix. 

a  Williams,  op.  cit.,  p.  91. 


ARCHEAN,  QUINISESEC  SCHISTS.  145 

Only  a  few  indications  of  the  original  structures  can  be  detected.  In 
a  few  small  areas  of  some  of  the  sections  the  structure  appears  to  have  been 
ophitic,  the  plagioclase  laths  occurring  as  radial  groups  in  a  matrix  of  chlo- 
rite, calcite,  and  bleached  amphibole.  In  most  of  the  sections,  however, 
no  traces  of  diabasic  structure  can  be  detected.  The  rocks,  tliough  much 
decomposed,  look  as  though  they  were  composed  of  crystals,  fragments, 
and  small,  almost  dust-like  grains  of  feldspar  in  a  grouudmass  that  yielded 
on  decomposition  new  plagioclase,  light-green  amphibole,  chlorite,  and 
calcite.  Most  of  the  fragments  are  certainly  portions  of  crystals  that  were 
crushed  when  the  rock  was  made  schistose,  but  there  are  many  others 
which  do  not  seem  to  be  due  to  mashing.  Some  of  these  have  concave 
outlines,  like  the  outlines  of  splinters  of  minerals  often  found  in  volcanic 
dust.  The  structure  thus  appears  to  resemble  more  closely  that  of  tuffs 
than  that  of  lavas. 

CHLORITE-SCHISTS. 

The  chlorite-schists  differ  from  the  very  schistose  greenstones  mainly 
in  the  fact  that  they  contain  no  original  plagioclase  nor  any  saussurite 
derived  from  this.  They  are  finely  schistose,  sometimes  fissile,  dark-green 
or  light-gray  rocks  containing  abundant  quartz  The  darker  varieties  are 
often  so  dark  and  so  very  fine  grained  that  they  look  very  much  like 
greenish-black  slates.  The  lighter-colored  varieties  resemble  very  soft, 
fine-grained  sericite-schists  or  talcose  schists. 

Under  the  microscope  the  dark-green  chlorite-schists  are  seen  to  be 
aggregates  of  green  chlorite,  calcite,  and  an  occasional  flake  of  a  sericitic 
mineral,  in  a  mosaic  of  quartz  and  secondary  albite. 

In  tlie  light-colored  schists  the  sericitic  mineral  and  calcite  are  more 
prominent  than  in  the  dai'ker  phases.     At  the  same  time  the  chlorite  has 
been  replaced  by  an  almost  colorless  variety. 
MON  XLVI — 0-t 10 


146  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

An  analysis  of  a  specimen  of  one  of  the  lightest  colored  of  these  rocks, 
taken  from  "the  western  corner  of  the  little  cove  just  below  the  Lower 
[Little]  Quinnesec  Falls,""  resulted  as  follows: 

Analysis  of  schist  from,  Little  Quinnesec  Falls. 

[Analyst,  R.  B.  Riggs.] 

SiO, - - 46.21 

AI2O3 - 18.  38 

FeA - :^-30 

FeO - - 3.90 

CaO - 6.28 

MgO 7.03 

NEjO 2.14 

KjO - - - 35 

HjO 3.82 

CO2 8.32 

Total 99.73 

TiO.,  not  determined. 

The  small  proportion  of  K2O  present  in  the  rock  would  seem  to  indicate 
that  the  sericitic  minei'al  is  paragonite  rather  than  sericite. 

Between  the  dark  and  the  light  varieties  of  the  schists  all  gradations 
are  met  with,  the  color  depending  upon  the  relative  proportions  of  the  dark 
chlorite  and  the  colorless  sericitic  mineral  developed. 

Many  of  the  chlorite-schists  of  all  kinds  occur  as  definite  bands  in  the 
schist  series.  They  are  not  so  related  to  the  massive  rocks  as  to  present 
undoubted  evidence  that  they  are  derived  from  these.  In  composition  and 
structure,  however,  they  are  identical  with  the  most  schistose  phases  of  the 
greenstone-schists  described  in  preceding  pages  (pp.  136-139)  as  the  end 
products  of  the  alteration  of  gabbros,  diorites,  diabases,  and  their  tuffs,  so 
that  little  doubt  can  be  felt  as  to  their  origin  from  similar  rocks. 

AMPHIBOLITES. 

The  amphibolites  are  limited  in  their  distribution  to  the  neighborhood 
of  the  great  granite  mass  in  Wisconsin.  They  neaxdy  always  occur  near 
the  contact  of  the  granite  with  the  greenstone-schists,  though  they  are 
occasionally  met  with  afe  narrow  selvages  along  the  side  of  granite  or 
granite-porphyry  dikes  where  these  cut  through  the  green  schists. 

The  only  careful  examination  of  any  part  of  the  contact  between  the 

"Williams,  op.  cit.,  p.  89. 


ARCHEAN,  QUINNESEC  SCHISTS.  147 

granite  and  the  suiTounding  greenstones  was  made  in  1894  by  A.  T. 
Lincoln.  Lincoln  followed  this  contact  abont  three-cjuarters  of  a  mile 
in  sees.  15  and  16,  T.  38  N.,  R.  20  E.,  Wisconsin,  a  short  distance  sou.th- 
west  of  the  Little  Quinnesec  Falls.  In  an  unpublished  thesis"  he  states 
that  "near  the  granite  the  greenstone  becomes  quite  schistose,  and  in 
some  places  becomes  a  typical  hornblende-schist.  Fragments  of  the 
greenstone  were  broken  oif  and  included  in  the  granite  mass  at  the  time 
of  its  intrusion.  In  some  parts  the  greenstone  is  very  intricately  ramified 
by  apophyses  of  granite." 

The  hornblende-schists  are  described  as  fine-grained,  lustrous,  black 
rocks,  traversed  l^y  small  veins  of  feldspar,  as  well  as  by  cracks  ramifying 
in  various  directions.  They  all  contain  more  or  less  altered  plagioclase  in 
considerable  quantities.  Some  are  porphyritic,  others  are  devoid  of 
phenocrysts. 

l^he  porjihyritic  schists,  when  examined  in  thin  section,  are  found — 

to  consist  chiefly  of  actinolite  crystals  so  arranged  as  to  give  the  rock  a  decided 
schistose  structure.  Distributed  throughout  the  hornblende  are  phenocrysts  of 
much-altered  feldspar.  These  have  quite  the  appearance  of  amjrgdules.  The}'  have 
altered  almost  completely  to  zoisite,  with  which  is  found  also  some  calcite.  *  *  * 
Sphene  is  quite  abundant,  some  of  which  still  retains  small  cores  of  ilmenite. 

The  n( mporphyritic  schists  differ  from  the  porphyritic  opes  merely  in 
the  absence  of  the  phenocrysts.  They  are  aggregates  of  hornblende  and 
comparatively  fresh  plagioclase. 

Since  all  of  these  schists  contain  large  quantities  of  plagioclase  they 
are  more  properly  designated  amphibolites  than  hornblende-schists.  The 
latter  are  characterized  by  the  possession  of  much  quartz  and  but  little 
feldspar.  Typical  hornblende-schists  have  not  yet  been  recognized  among 
the  Quinnesec  schists,  though  they  are  found  in  fair  abundance  in  tlie 
gneiss-schist  complex  north  of  the  Menominee  trough. 

From  the  nature  of  the  amphibolites  and  their  intimate  association  witli 
the  ordinary  types  of  the  greenstone- schi.sts,  it  may  fairly  be  concluded 
that  they  were  derived  from  the  same  kinds  of  basic  igneous  rocks  as  were 
the  greenstone-schists  and  the  chlorite-schists.     Their  exclusive  occui-rence 

«  Lincoln,  A.  T.,  On  the  greenstone  area  in  the  vicinity  of  the  Lower  Quinnesec  Falls,  Wisconsin 
side;  a  thesis  submitted  for  the  degree  of  B.  S.  in  the  group  course  in  mineralogy,  University  of 
Wisconsin,  1894.     (Not  published. ) 


148  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

near  granite  contacts  would  indioate  that  they  owe  their  peculiar  character 
to  their  proximity  to  the  intrusive.  In  other  words,  they  are  greenstones 
that  have  been  subjected  not  only  to  dynamic  metamorphism,  but  to 
contact  alteration  as  well. 

Types  of  rocks  intermediate  in  character  between  the  amphibolites  and 
the  greenstone-schists  are  found  in  profusion  along  the  banks  of  the 
Menominee  River  at  the  rapids  known  as  the  Horserace.  Here  the  basic 
schists  are  intruded  by  acid  rocks,  to  which  fact  their  peculiar  features  may 
be  ascribed  (see  pp.  158-159). 

OKKJIA  OF  THE  BASK:  SCHISTS. 

Fi'om  the  field  and  laboratory  study  of  the  basic  schists,  one 
must  conclude  with  Williams  that  they  are  squeezed  igneous  rocks,  and 
their  tuifs,  which,  on  account  of  the  squeezing  to  which  they  have  been 
subjected,  have  lost  in  many  instances  all  traces  of  their  original  structure 
and  nearly  all  of  their  original  mineral  components.  From  the  nature  of 
the  products  that  liave  arisen  from  the  alteration  of  these  components  we 
are  led  to  believe  that  the  original  rocks  were  basic.  In  a  few  cases  the 
original  composition  and  the  original  structure  of  the  schists  can  be  recon- 
structed from  the  evidences  still  remaining,  and  in  these  cases  it  may  be 
safely  asserted  that  the  original  rocks  were  gabbros,  diorites,  diabases,  and 
perhaps  basalts  among  the  crystalline  varieties  and  diabase  tuflp  among  the 
fragmental  varieties.  MaiiA'  of  the  schists  that  are  without  a  distinct 
igneous  structure  are  so  closely  associated  with  basic  rocks  which  are  almost 
massive,  and  are  connected  with  these  by  such  intimate  gradational  phases, 
that  no  doubt  can  be  felt  as  to  their  origin.  These  schists  are  unquestion- 
ably squeezed  gabbros,  diorites,  diabases,  and  other  basic  rocks.  They 
are  identical  in  every  respect  with  many  of  the  schists  whose  field  relations 
do  not  directly  connect  them  with  massive  eruptives,  and  thus  lend  force 
to  the  view  that  these  latter  schists  are  likewise  squeezed  igneous  rocks. 

The  conditions  under  which  the  igneous  rocks  consolidated  are  not 
plain  in  all  cases.  Some  of  the  more  massive  gi-eenstones  were  certainly 
originally  dikes.  Many  of  the  others  and  most  of  the  schists  were  prob- 
ably lavas  or  sheets,  or  tuffs.  Dr.  Williams  thinks  that  there  is  considerable 
evidence  to  show  that  the  Menominee  greenstones  solidified  at  the  surface 
under  subaerial  or  subaqueous  conditions.  ' 


ARCHEAN,  QUINNESEC  SCHISTS.  149 

In  the  Menominee  Valley  this  evidence  consists  (1)  of  the  fine  texture  of  the 
rocks;  and  (2)  of  the  alternation  of  bands  of  different  types,  which  probably  in  theii 
original  position  represented  successive  flows.  Fineness  of  grain  is  universal  in  the 
Menominee  greenstones,  and  we  may  be  certain  that  it  was  a  pT-imaiy  feature  in 
spite  of  the  extensive  alteration  of  these  rocks.  It  is  especially  noticeable  in  the 
case  of  the  gabbro,  which  is  almost  always  a  coarse-grained  rock  when  it  has  solidified 
at  any  depth.  The  succession  of  massive  beds,  like  the  pale  gabbros  and  the  dark 
diabases  seen  at  Lower  [Little]  Quinnesec  Falls,  are  difficult  to  account  for  except  by 
supposing  that  they  were  once  horizontal  sheets  whicli  flowed  one  over  another,  and 
which  were  subsequently  elevated  into  their  present  nearly  vertical  position.  Traces 
of  tuff  material  are  not  as  distinct  here  as  in  the  Marquette  region,  although  indica- 
tions of  their  existence  are  by  no  means  wanting.  We  might  reasonably  expect 
that  any  original  scoriaceous  or  amygdaloidal  structure  would  have  disappeared  in 
the  course  of  the  profound  chemical  changes  through  which  these  greenstones  have 
passed." 

Since  the  above  was  wiitten  undoubted  tuffs  have  been  discovered  in 
the  Menominee  district  in  the  vicinity  of  the  Little  and  the  Big- 
Quinnesec  Falls,  and  in  Wisconsin  about  a  mile  southwest  of  the  lower 
falls,  and  over  a  large  area  in  the  latter  State  several  miles  south  of  the 
river,  opposite  the  city  of  Norway.  This  discovery  adds  additional  strength 
to  Williams's  view,  which  must  therefore  be  accepted  as  probably  true. 

ACID   IXTKCSITES   AND   THEIR   DEBITED   SCHISTS. 

The  acid  rocks  associated  with  the  basic  schists  in  Michig-an  are 
limited  principally  to  the  neighborhood  of  the  Horserace  Rapids  and  the 
Big  Quinnesec  Falls.  They  include  gneissoid  granites,  porphyritic 
gneisses  or  porphyroids,  felsite-schists,  sericite-schists,  and  probably 
paragonite-schists.  The  sericite-schists  and  paragonite-schists  are  found 
also  associated  with  the  greenstone-schists  in  other  portions  of  tiie  southern 
area. 

The  gneisses,  porphyroids,  and  felsite-schists  are  so  similar  in  composi- 
tion to  the  Wisconsin  granite,  which  is  only  about  three-quarters  of  a  mile 
from  the  Menominee  River  at  the  Little  Quinnesec  Falls,  that  they  may 
be  regarded  as  its  apopliyses.  Some  of  the  larger  of  the  gneiss  bands  may 
be  traced  practically  continuously  into  the  granite  mass.  The  sericite- 
schists  and  the  paragonite-schists  in  many  places  pass  by  a  continuous  series 
of  gradational  phases  into  the  felsite-schists.  Hence  it  seems  probable 
that  these  are  also  extensions  of  the  granite. 

Williams,  op,  cit.,  pp.  200-201. 


150  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Structurally  the  acid  rocks  are  in  the  form  of  dikes  or  sheets.  Some 
of  them  cut  across  the  bands  of  basic  schists  in  any  direction.  These  are 
unquestionably  dikes.  The  greater  portion,  however,  occur  in  bands  that 
trend  parallel  to  the  direction  of  the  bands  of  basic  schists  suiTOunding- 
them.  These  may  be  either  intrusive  sheets  or  they  ma,j  be  dikes  which 
at  the  present  surface  happen  to  follow  the  bedding  planes  of  the  schist 
bands.  Below  the  surface  they  may  all  cut  across  the  schist  bands,  as 
some  are  known  to  do.  The  rocks  of  these  two  classes  comprise  gneisses, 
porphyroids,  felsite-schists,  and  some  of  the  sericitic  schists.  The  finer- 
grained  rocks  are  always  associated  with  coarser-grained  gneisses  or 
gneissoid  porphyries.  A  third  class  of  acid  schists  may  have  been  volcanic 
flows  These  comprise  some  of  the  sericite-schists  and  paragonite-schists. 
The}^  occur  in  definite  bands  running  parallel  to  the  bands  of  the  basic 
schists.  They  occur  sporadically  in  the  midst  of  the  greenstone-schists, 
and  are  not  associated  with  any  forms  of  rocks  regarded  as  apophyses  of  the 
granite. 

All  of  the  acid  members  of  the  Quinnesec  schists  are  more  or  less  schis- 
tose. The  most  massive  granite-like  dikes,  and  even  the  peripheral  portion 
of  the  granite  boss,  exhibit  distinct  foliation.  In  the  porphyritic  varieties  • 
the  finer-grained  groundmass  is  very  strongly  schistose,  while  the  pheno- 
crysts  are  elongated  into  lenticular  masses.  The  felsites  and,  in  general, 
the  fine-grained  rocks  are  much  more  distinctly  schistose  than  the 
coarser-grained  ones,  and  many  of  them  are  fissile. 

The  schistosity  of  all  the  acid  rocks,  like  that  of  the  basic  schists,  is 
clearly  the  result  of  pressure  acting  after  the  intrusive  masses  assumed 
their  present  position,  since  in  some  cases,  at  least,  the  direction  of  the 
.schistosity  is  inclined  to  the  direction  of  the  walls  inclosing  the  intrusion. 

Gneissoid  granite  and  granite-gneisses. — The  mass  of  the  rock  constitut- 
ing the  boss  in  Wisconsin  is- — 

i\  typical  coarse-^raiued  granitite,  with  a  decided  tendencj'  to  a  porphyritic  struc- 
ture. *  *  *  When  examined  under  the  microscope  the  macroscopic  diag'nosis  is 
found  to  be  correct,  and  several  additional  points  of  interest  are  brouj^ht  to  light. 
The  oldest  constituents  are  zircon  and  apatite;  both  quite  abundant  in  the  form  usual 
in  granitic  rocks.  Iron  oxide  seems  to  be  almost  absent  as  an  original  constituent, 
though  it  is  found  in  some  of  the  altered  micas.  The  biotite,  the  oiify  mica  present, 
is  not  abundant.  It  is  invariablj'  bleached  to  a  green  color  by  the  reduction  of  its 
iron  to  the  ferrous  state.     It  contains  abundant  inclusions  of  apatite,  zircon  (around 


ARCHEAN,  QUINNESEC  SCHISTS.  151 

which  are  pleochroic  aureoles),  and  some  secondary  magnetite.  No  trace  of  either 
hornl)lende  or  pyroxene  was  observed.  Sphene,  however,  is  present,  as  are  also  a 
few  sharp  crystals  of  a  dark  grayish-blue  tourmaline.  The  principal  interest  of  this 
rock  attaches  to  its  feldspar  and  quartz.  They,  together,  make  up  nearly  the  whole 
mass,  and  exhibit  in  a  remarkable  degi'ee  the  effects  of  pressure.  The  feldspar  is  of 
three  kinds — normal  plagioclase  (oligoclase),  unstriated  orthoclase,  and  microcline. 
The  relationship  of  these  species  of  feldspar  is  a  suggestive  one.  Both  the  oligo- 
clase and  the  orthoclase  are  always  altered  to  a  fine  micaceous  or  kaolinitic  product 
which  is  particularly  abundant  in  the  center  of  the  crystals,  a  zone  of  the  unaltered 
mineral  being  often  preserved  around  the  edge.  The  microcline,  on  the  other  hand, 
almost  never  shows  any  indication  of  alteration. 

It  is  always  clear  and  fresh  in  appearance,  but  its  twinning  lamella  are  bent  or 
curved  and  bear  eveiy  sign  of  having  been  secondarily  developed.  *  *  *  The 
large  original  feldspar  crystals  show  a  peripheral  gi'anulation,  '•'  *  *  and  where 
they  have  been  fissured  their  cracks  are  filled  with  a  new  crystallization  of  plagioclase, 
orthoclase,  and  quartz.  None  of  these  minerals  shows  an}'  signs  of  chemical  alteration 
and  microcline  is  never  to  be  found  among  them.  Thus  is  produced  a  good  example 
of  what  Tornebohm  has  called  a  mortar  structure  ("Mortel-Structur").  In  this  sec- 
ondary cement-like  aggregate  a  micropegmatitic  intergi'owth  of  quartz  and  feldspar 
is  quite  common,  and  calcite,  in  good-sized  individuals,  is  by  no  means  rare. 

The  original  quartz  of  this  granite  also  shows  many  indications  of  having  been 
squeezed.  The  crystals  or  grains  often  have  an  undulatory  extinction,  while  larger 
grains  are  broken  and  the  fragments  are  more  or  less  displaced." 

The  coarser-grained  gneissic  granites,  augen-gneisses,  and  porphyries 
incorporated  with  the  green  schists  are  identical  in  composition  with  por- 
tions of  the  great  granite  mass.  The  rocks  have  in  many  cases  undergone 
considerable  chemical  change,  and  have  been  subjected  to  a  great  deal  of 
crushing.  Nevertheless  they  can  all  be  recognized  as  having  differed  orig- 
inally from  the  granite  only  in  structure.  Nearly  all  appear  to  have  been 
porphyritic.  Many  of  them  have  lost  their  porphyritic  character  by  the 
crushing  of  their  original  components  and  the  crystallization  of  new  material 
between  the  crushed  fragments.  The  mashing,  together  with  recrystalliza- 
tion,  has  changed  the  phenocrysts  of  feldspar  into  the  augen  of  tlie  augen- 
gneisses;  it  has  produced  well-characterized  gneisses  from  quartz  porphy- 
ries; and  has  changed  the  quartz  phenocrysts  of  the  latter  into  granular, 
lenticular  aggregates  of  this  mineral. 

Williams  describes  a  band  of  granite-porphyry  cutting  the  greenstone- 
schists  on  the  south  side  of  the  basin,  just  below  the  Horserace  Rapids.    The 

"Williams,  op.  cit.,  pp.  111-112. 


152  THE  MENOMINEE  IRON-BEAKING  DISTRICT. 

center  of  the  baud  is  a  massive  gray  porpliyritic  rock.  This  grades  on 
both  sides  into  a  well-characterized  fine-grained  gneiss,  resembling  a 
o-rannlite.  The  central  portion  of  the  band  consists  of  large  crystals  of  a 
zonal  plagioclase  embedded  in  a  granular  mosaic  of  clear,  colorless, 
untwinned,  and  probably  newly  crystallized  grains  of  audesine,  associated 
with  browu  leaflets  of  biotite.  Apatite,  zircon,  and  a  reddish  pleochroic 
sphene  are  also  present  in  small  crystals.  Calcite  is  also  abundant. 
Though  the  rock  is  fresh  and  appears  to  be  unaltered,  the  presence  of 
calcite  indicates  that  it  has  suffered  a  change  from  its  original  character. 
The  audesine  is  probably  one  of  the  new  products  formed." 

The  gneissic  portion  of  the  band  resembles  the  groundmass  of  the 
central,  jjorphyritic  phase.  The  chief  difference  is  the  banded  appearance 
of  the  gneiss,  produced  by  the  parallel  arrangement  of  the  biotite  and  the 
alternation  of  layers  of  different-sized  grains.  Tourmaline  and  rutile  are 
present  in  some  sections.  Remains  of  plagioclase  phenocrysts  are  observed 
in  others,  but  the  porphyritic  crystals  have  been  nearly  destroyed  by 
granulation. 

An  analysis  of  the  most  massive  portion  of  the  band  was  made  by  Mr. 
R.  B.  Riggs.  It  disclosed  the  fact,  already  intimated  above,  that  the  rock 
is  more  nearly  a  diorite  than  a  granite  in  composition." 

Analysis  of  massive  portion  of  hand  of  granite-porphyry  near  Horserace  Rapids. 

SiO, 54.83 

AlA - - -  25.49 

FeA - - ^■''^ 

FeO  - - - 1-65 

CaO - - «-08 

MgO  .  - 1-96 

Na/) - - -  -  -  5.  69 

K,0  -- 1-87 

H,0 - ---- 118 

CO, - ^ 

Total 100.54 

Other  specimens  of  the  granite-porphyry  are  more  like  granite  than 
the  one  just  described.  In  these  quartz  and  orthoclase  both  occur  as 
phenocrysts.  Biotite  and  nniscovite  are  present  in  the  groundmass,  the 
latter  being  derived  partly,  at  any  rate,  from  orthoclase.     The  quartz  phen- 

oWilUams,  op.  cit.,  p.  113. 


ARCHEAN,  QUINNESEC  SCHISTS.  153 


ocrysts  are  usually  granulated — sometimes  throughout  their  entire  masses, 
often  only  peri[)heral]y. 

The  augen-g-neisses  difter  from  the  porphyritic  gneissic  granite  mainly  in 
the  extent  of  the  mashing  which  they  have  suffered.  They  are  well  banded 
01  gneissic  through  the  arrangement  of  the  constituents  of  the  groundmass, 
notably  biotite  and  muscovite,  in  parallel  directions.  Phenocrysts  have 
disappeared  by  granulation,  and  have  been  deformed  into  flattened  bodies, 
ajid  new  crystallizations  of  feldspar  or  quartz  have  been  deposited  in 
masses  with  triangular  cross  sections  at  the  ends  of  the  long  axes  of  the 
flattened  grains.  The  crystal  forms  of  the  phenocrysts  have  thus 
disappeared,  and  lenticular  bodies  have  resulted. 

One  of  these  rocks  from  a  dike  at  the  upper  end  of  the  Horserace 
Rapids,  on  the  Michigan  side  of  the  river,  was  also  analyzed  by  Mr.  Riggs. 
Its  composition  is  that  of  a  granitite." 

Analysis  of  gr emit ite  from  uppei^  end  of  Horsefrace  Rapids. 

SiO^. 67.77 

Al^Os 16. 61 

FejO,, 2. 06 

FeO 1. 96 

CaO 1.87 

MgO 1.26 

Na^O 4.  35 

K^O 2.35 

HjO 1 .  69 

CO2 19 

Total 100. 11 

Por])hyries  and  felsites  and  their  schistose  ^ihases. — The  quartz-porphyries 
are  now  to  all  intents  and  purjjoses  like  the  groundmass  of  the  augen- 
gneisses,  with  the  addition  of  rounded  or  dihexhedral  quartz  grains  and  an 
occasional  phenocryst  of  plagioclase.  They  are  3^ellowish-gray  or  reddish 
schists,  with  a  greasy  feeling.  The  components  are  the  same  as  those  of 
the  augen-gneisses,  but  muscovite  is  much  more  abundant  in  them  than  in 
the  latter  rocks.  The  mineral  that  was  originall}^  biotite  is  often  now 
represented  by  chlorite.  All  the  larger  grains  are  fractured  or  granulated, 
and  the  smaller  ones  are  flattened.  Nests  of  calcite  are  often  abundant. 
An  analysis  of  one  of  these  rocks  by  Riggs  showed  it  to  belong  unques- 
tionably with  the  granite  magmas.'' 

"Williams,  op.  cit,  p.  119.  ''Ibid.,  p.  121. 


154  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Analysis  of  quartz-po7'phyrt/  Jrom  J3ig  Quinnessec  FaUs. 

SiOj - - •- 66. 69 

AlA - - 16.69 

FeA -     2.06 

FeO 93 

CaO - 1  •  40 

MgO - -  -  -     1.15 

Na^O 2.46 

K,0 5.23 

H^O - 1.  70 

CO2 1.'12 

Total 99.  73 

The  schistose  felsites  differ  from  the  schistose  quartz-porphyries  only 
in  texture.  They  are  very  fine-grained  aggregates  of  the  same  minerals 
that  characterize  the  matrix  of  the  porphyries.  Originally  they  may  have 
been  felsitic  apophyses  of  the  granite  mass,  or  possible  porphyritie 
microgranites,  that  were  later  so  thoroughly  crushed  that  their  constituents 
have  been  completely  granulated  into  minute  flattened  particles  which  are 
now  cemented  together  by  newly  deposited  material.  The  felsites  as  they 
now  exist  are  very  schistose.  Muscovite  is  abundant  in  them  and  this  is 
always  so  arranged  in  the  thin  section  that  the  long  axes  of  its  shreds  are 
parallel  to  the  plane  of  flattening  of  the  other  components. 

SERICITE-SCHISTS. 

All  the  acid  rocks  thus  far  discussed  are  plainly  younger  than  the  green- 
stone-schists which  they  intrude.  From  their  nature  and  the  relations  of 
some  of  them  to  the  granite  mass  south  of  the  Menominee  River  we  are  led 
to  conclude  that  they  are  apophyses  of  this  mass.  A  few  other  schists  may 
also  be  acid  rocks.  These  are  so  intimately  incorjjorated  with  the  green 
schists  that  they  appear  to  be  integral  portions  of  the  schist  series.  They 
always  occur  in  bands  parallel  to  the  bands  of  basic  schists,  and  never  cross 
the  latter.  These  rocks  are  the  light-colored  white  or  gray  micaceous  schists 
called  by  Williams  "silvery  schists."  In  composition  they  are  mainly 
sericite-schists.  Williams  regarded  them  as  specially  metamorphosed  basic 
schists.  Some  of  the  light  schists  associated  with  the  dark-green  ones  may 
be  of  this  character,  but  these  are  light-colored  chlorite-schists.  The  sericite- 
schists  are  of  a  different  character.  Under  the  microscope  they  are  seen  to 
be  composed  of  quartz  grains,  sericite  scales,  and  chlorite  shreds  arranged 
in  a  parallel  manner.      No  feldspar-  is  noticeable  in  them,   but   calcite  is 


ARCHEAN,  QUINNESEC  SCHISTS.  155 

abundant.  As  at  present  constituted  the  rocks  are  unquestionably  acid. 
Though  no  analyses  are  at  hand  to  substantiate  tliis  statement,  the  abun- 
dance of  quartz  and  sericite  noted  in  the  slides  leaves  no  doubt  as  to  its 
correctness. 

These  acid  schists  probably  represent  acid  flows  contemporaneous  with 
the  basic  flows  with  which  they  are  associated.  Their  source  is  not  yet 
known.  They  are  so  rare  that  they  constitute  but  a  small  fraction  of  the 
Quinnesec  schist  series,  which  is  essentially  a  set  of  schists  produced  by 
mashing  from  a  succession  of  layers  of  basic  lavas  and  tufis. 

INTERESTING   LOCALITIES. 

Grood  exposures  of  the  Quinnesec  schist  series  and  their  intrusions  may 
be  seen  at  the  Sturgeon  Falls,  the  Big  and  the  Little  Quimiesec  Falls, 
and  along  the  Horserace  Rapids.  At  the  various  falls  only  the  basic  mem- 
bers of  the  series  are  present,  and  a  few  minor  bands  of  sericite-schists, 
except  that  at  the  Big  Quinnesec  Falls  there  are  a  few  bands  of  gneiss. 
At  the  Horserace  Rapids  the  basic  schists  are  also  mainly  in  evidence,  but 
acid  intrusions  are  also  common.  Moreover  the  basic  schists  are  of  a  different 
character  from  those  at  the  several  falls.  In  appearance  they  are  more 
crystalline  than  the  latter.  In  composition  they  are  more  hornblendic  and 
less  chloritic.  The  peculiar  character  of  the  schists  along  this  stretch  of 
the  river  he  been  ascribed  in  previous  pages  (pp.  14(i-148)  to  the  eff"ect  of 
the  granitic  intrusions. 

Sturgeon  Falls. — The  most  abundant  rock  at  the  Sturgeon  Falls  is  a 
coarse-grained,  light-gray  massive  saussurite-gabbro.  It  forms  the  first  bar- 
rier over  which  the  water  plunges  in  the  series  of  cascades  that  constitute 
the  falls  (see  PI.  X,  A),  and  again  it  occurs  at  the  lower  end  of  the  basin 
below  the  falls.  The  falls  proper  occupy  a  stretch  of  several  hundred  feet 
along  the  river.  The  stream  here  is  narrow  and  its  channel  is  gorge-like. 
Precipitous  walls  of  the  gabbro  form  the  banks  and  these  are  practically 
continuous.  At  the  lower  end  of  the  narrows  the  rocks  are  slightly  schistose, 
but  still  retain  the  gabbroitic  texture.  About  midway  between  the  upper 
and  the  lower  portions  of  the  exposure  several  narrow  bands  of  fissile,  silky 
sericite-schist  penetrate  the  gabbro  and  appear  midwaj'  of  the  east  wall. 
Between  two  of  these  is  a  narrow  band  of  the  massive  rock  exactly  like  the 
gabbro  of  the  barrier.     Intimate  gradations  exist  between  the  schists  and 


156  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  massive  gabbro.  Although  the  gradation  is  much  more  rapid  in  some 
places  than  in  others,  no  sharp  line  of  demarcation  can  be  drawn  lietween 
the  schistose  and  the  massive  rocks.  From  the  field  relations  of  the  two 
phases  it  is  evident  that  the  schists  represent  mashed  and  altered  forms  of 
the  gabbro. 

Little  Quinnesec  Falls. — At  the  l^ittle  Quinnesec  Falls  a  great  width  of 
basic  schists  and  massive  rocks,  best  seen  in  the  west  or  Wisconsin  side  of 
the  river,  stretch  up  and  down  the  stream  for  a  distance  of  about  1,500 
feet.  The  succession  is  made  up  of  dark-green  chlorite-schists,  light- 
colored  sericite-schists,  light-gray  schistose  diabases,  and  several  beds  of 
fairly  massive  dark-green  diabase.  The  light  schists  grade  into  the  lighter- 
colored  diabases,  and  the  darker  ones  into  the  dark  diabases  So  gradual 
Is  the  transition  between  the  aiassive  and  the  schistose  phases  of  the  rocks 
and  so  intimate  is  the  relation  of  the  two  varieties  that  there  is  no  escape 
from  the  conviction  that  the  former  are  but  schistose  ])ortions  of  the  latter. 
At  the  immediate  foot  of  the  falls  on  the  east  side  is  an  exposure  of  sericite- 
scliist  of  the  kind  that  is  supposed  to  have  been  derived  from  an  acid  bed. 
It  is  a  little  more  distinctly  separable  from  the  bands  of  diabase  between 
wliicli  it  lies  than  are  the  light-colored  schists  farther  downstream,  but 
nevertheless  it  apparently  grades  into  them. 

On  the  Michigan  side  of  the  river,  near  the  water's  edge,  much  of  the 
rock  is  essentially  like  that  on  the  Wisconsin  side,  but  in  addition  there  is 
present  just  below  the  falls  and  extending  from  this  point  to  the  bridge  over 
the  falls  the  thick  band  of  conglomeratic  greenstone  refeired  to  by 
Wadsworth  (p.  102).  This  is  doubtless  a  tuif  bed.  Sericite-schists  and 
bands  of  fairlv  massive  basic  rocks  traverse  the  tuft'.  The  former  were 
regarded  by  Wadsworth  as  dikes  and  by  Williams  as  special  phases  of  the 
green  schists.  The  bands  of  basic  rock  were  described  by  Williams  as 
dikes.  By  Wadsworth  it  was  thought  that  they  might  be  finer-grained  and 
more  massive  phases  of  the  tuft"  beds.  On  both  sides  of  the  river  the  strike 
of  the  schistosity  of  the  schists  and  of  the  trend  of  the  more  massive  bands 
associated  with  them  is  a  little  south  of  west.  The  dip  is  about  vertical. 
All  the  massive  or  nearly  massive  bands  of  this  series  consist  of  some  form 
of  diabase,  which  is  usually  saussuritized.  On  the  Michigan  side  of  the 
river,  however,  and  a  little  distance  back  from  its  bank  is  a  high,  abrupt 
ridge  composed  of  a  dark  coarse-grained  gabbroitic  rock,  which  is  uniform 


ARCHEAN,  QUINNESEC  SCIHISTS.  lo7 

in  composition  and  structure  throughout  the  entire  length  of  the  ridge. 
Near  the  western  end  of  the  ridge  the  rock  is  composed  of  a  light-greenish 
gray  matrix  in  which  lie  porphyritic  crystals  of  white  feldspar  and  black 
hornblende.  This  is  the  type  called  by  Williams  "diorite."  At  its  south- 
east end  the  rock  is  green  and  fine  grained.     It  contains  no  phenocrysts. 

This  is  compact  and  massive  in  structure,  but  everywhere  profoundly  seamed 
and  jointed.  It  is  out  l\y  cross  gashes  and  parted  joints,  and  gives  everj'  indication 
of  having  been  pulled  or  crushed — at  all  events,  of  having  been  subjected  to 
enormous  mechanical  strains.  The  joints  and  seams  often  run  in  many  different 
directions,  producing  a  regular  breccia  without  cement.  The  rock  is  also  much 
slickensided,  frequently  so  much  so  as  to  produce  a  schistose  structure.  The  layers 
thus  formed  sometimes  bend  around  more  massive  cores,  which  seem  to  have 
resisted  the  rubbing  action. 

The  formation  of  what  are  above  described  as  "cross-gashes"  is  very  curious. 
At  times  the  entire  face  of  the  rock  wall  is  scarred  with  approximately  parallel 
gaping  seams,  closely  resembling  the  rents  formed  in  moderatel}^  dry  clay  or  putty 
when  this  is  stretched.  A  single  opening  does  not  extend  for  any  great  distance, 
but  a  great  number  of  them  of  all  dimensions,  closely  crowded  together,  may 
produce  an  irregular  sort  of  foliation.  *  *  *  These  gashes  seem  to  have  been  pi"o- 
duced  b}-  a  stretching  of  the  rock  or,  what  amounts  to  the  same  thing,  by  a  bulging 
perpendicular  to  the  action  of  some  great  pressure.  They  resemble  the  "  klaffende 
Risse,"  described  by  Heim,  in  the  Alps.  *  *  *  Tj^g  edges  of  the  seams  are 
ragged,  as  though  they  had  been  formed  by  a  forcible  tearing  asunder  of  the  rock 
after  it  was  solid.  They  are  often  filled  with  subsequent  infiltrations  of  secondary 
minerals. like  calcite  or  quartz,  but  more  frequently  they  are  open." 

Big  Quinnesec  Falls. — At  the  Big  Quinnesec  Falls  and  the  Horse- 
race Rapids  there  is  about  a  mile  of  continuous  exposure  on  both  sides  of 
the  river.  The  barrier  rock  of  the  falls  is  a  medium-grained,  gray,  saussu- 
ritized  gabbro,  which  is  in  places  almost  massive.  On  the  Wisconsin  side 
of  the  rivei'  the  pale  gabbro  can  be  seen  grading  into  a  light-green  schist; 
and  again,  just  below  the  engine  house,  on  the  Michigan  side  of  the  falls,  it 
can  be  traced  into  the  silvery  hydro-micaceous  or  sericite-schists  and  into 
green  chlorite-schists.  At  the  lower  extremity  of  the  basin,  below  the  falls, 
is  an  exposure  that  juts  into  the  river  from  the  Wisconsin  side.  The  main 
portion  of  the  exposure  is  composed  of  a  green  massive  rock,  which  is  a 
good  illustration  of  a  diabase  that  has  suffered  epidotization  and  chloritiza- 
tion.    In  places  it  is  crossed  by  bands  of  schist,  that  grade   imperceptibly 

"^VilIiams,  op.  cit.,  p.  80. 


158  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

iuto  the  massive  rock.  Farther  up,  ou  the  Michigan  side,  is  a  series  of 
exposures  of  practically  the  same  rocks.  Schistose  phases  are  more  couiiuou 
in  these  exposures  than  in  the  one  on  the  Wisconsin  side.  It  is  in  these 
rocks  that  the  fine  intergrowths  of  magnetite  and  rutile  described  by 
Williams"  occur 

Horserace  Rapids. — At  the  Horserace  Rapids  the  rocks  are  markedly 
different  from  any  others  occurring  in  the  Michigan  area  of  the  Quinnesec 
schists.  They  are,  however,  like  many  of  those  near  the  granite  mass  in 
Wisconsin.  During  times  of  high  water  the  Horserace  is  a  foaming,  dash- 
ing cataract,  rushing  between  two  low  but  steep  walls  of  dark-green  rocks, 
crossed  here  and  there  by  dark  pink  bands.  When  the  water  is  low, 
shelving  banks  extend  streamward  from  the  bases  of  the  cliffs,  and  along 
these  the  relations  of  the  various  rocks  to  one  another  may  easily  be 
studied. 

Between  the  Big  Quinnesec  Falls  and  the  lower  portion  of  the 
rapids  is  a  short  stretch  of  comparatively  quiet  water  bordered  by  dark- 
green  massive  and  schistose  greenstones  like  those  in  the  basin  below  the 
falls.     In  places  these  are  cut  by  bands  of  pink  gneiss. 

The  rapids  have  excavated  their  channel  through  rocks  of  an  entirely 
different  character.  Here  the  greater  portion  of  the  river's  banks  consists 
of  a  coarse,  gray  diorite,  speckled  by  large,  and  often  glistening,  crystal 
faces  of  dark-green  hornblende,  which  sometimes  measure  1  or  2  inches 
in  diameter.  Occasionally  biotite  flakes  are  discernible  in  the  hand  speci- 
men, and  minute  silvery  glistening  scales  of  talc.  This  mineral  coats  the 
walls  of  all  cracks  and  fissures  in  the  rock  and  dots  the  faces  of  the  horn- 
blende crystals.  In  many  places  the  basic  rocks  have  a  distinctly  gneissic 
structure.  The  schistose  rock  is  dai'ker  than  the  more  massive  phase  and 
^jresents  a  more  crystalline  appearance.  Other  exposures  consist  of  fibrous 
dark  amphibolite  and  others  of  dark-green  chlorite-schists.  The  latter  often 
traverse  the  massive  diorites  and  grade  into  them  on  both  sides.  In  general 
the  basic  rocks  along  the  Horserace  are  coarser  grained,  darker  colored, 
and  more  crystalline  than  elsewhere  along  the  river. 

Another  respect  in  which  the  Horserace  exposures  differ  from  those 
elsewhere  is  in  the  presence  of  numerous  acid  rocks.     These  occur  in  bands 

a  Williams,  G.  H.,  The  greenstone-schist  areas  of  the  Menominee  and  Marquette  regions  of  Michi- 
gan: Bull.  U.  S.  Geol.  Survey  No.  62,  1890,  pp.  99-101;  and  Neues  Jahrbuch  fiir  Jlin.,  etc.,  1SS7, 
Cf.  also  A.  Cathrein,  ibid.,  1888,  vol.  2,  p.  151. 


U.    S.    GEOLOGICAL    SURVEY 

MONOGRAPH 

XLVi 

PL. 

XI 

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A.      HORSERACE   RAPIDS    DURING    HIGH    WATER. 
Looking  downstream  from  Chicago,  Milwaukee  and  St,  Paul  Railway  bTidge, 


li.      LOG   JAM    IN    HORSERACE    RAPIDS. 
Looking  downstream  fiom  Chicago,  Milwaukee  and  St.  Paul  Railway  bridge. 


ARCHEAN,  QUINNESEC  SCHISTS.  159 

of  varying  width,  generally  conforming  to  the  foliation  of  the  greenstones. 
The  bands  are  sometimes  composed  of  a  massive  pink  granite.  Usually, 
however,  they  are  gneissic  or  schistose,  and  the  rocks  are  gneisses, 
augen-gneisses,  felsites,  or  other  acid  types  already  referred  to  in  previous 
pages.  In  texture  these  rocks  are  usually  coarse  grained,  but  some  of  them 
are  very  tine  grained.  In  color  the}'  vary  between  gray  and  red,  pink 
shades  predominating.  Although,  as  has  been  stated,  the  acid  bauds 
usually  trend  conformably  with  the  foliation  of  the  greenstones,  there  are 
enough  exceptions  to  this  rule  to  prove  conclusively  that  many  of  the  bands 
are  intrusive.  On  the  shore  of  the  little  cove  in  the  Michigan  side  of  the 
river  at  the  head  of  the  Horserace,  the  intrusive  character  of  one  of  these 
bands  is  plainly  shown.  Two  bands  of  gneiss  cut  the  greenstones.  One 
traverses  the  schists.  At  another  point  farther  downstream  a  band  of 
gneiss  ends  abrujjtly  in  the  green  schists  and  sends  out  short  apophyses 
into  them.  A  few  otlier  instances  of  similar  character  may  be  seen  at  sev- 
eral places  on  the  Michigan  side  of  the  rapids,  but  tlie  general  tendency 
seems  to  have  been  for  the  acid  intrusions  to  follow  the  planes  of  foliation 
of  the  schists. 

THE  WESTERN   AREA. 
DISTRIBUTION. 

The  western  Quinnesec  schists  occuj^y  a  triangular  area  of  about  5 
square  miles,  in  Michigan,  extending  from  about  the  center  of  sec.  15,  T. 
40  N.,  R.  30  W.,  Michigan,  westward  to  the  Menominee  River.  Where  it 
crosses  the  river  the  belt  is  about  3  miles  wide.  After  crossing  the  strean 
into  Wisconsin,  it  gradually  widens  into  a  broad  expanse,  the  boundaries  of 
which  are  at  present  unknown.  The  Fourfoot  Falls  are  at  the  southern  side 
of  the  area  where  it  crosses  the  Menominee  River,  and  the  old  Indian  village 
of  Badwater  is  at  its  northern  limit.  The  portion  of  the  area  away  from 
the  river  is  outlined  by  a  few  small,  scattered  exposures  rising  as  little 
knobs  above  the  soil  and  glacial  sands. 

TOPOGRAPHY. 

The  topography  of  the  area  underlain  by  the  schists  possesses  no 
distinctive  peculiarities.  At  its  east  end  are  several  small  rugged  knobs 
with  exposures  of  greenstones  on  their  slopes,  and  at  the  western  edge 
along  the  river  are  other  knobs,  some  of  which  are  rough  and  bare.     The 


160  THE   MENOMINEE  IRON-BEAKING  DISTRICT. 

rest  of  the  area  is  covered  with  glacial  deposits  that  are  so  thick  as  to 
produce  the  usual  assemblage  of  hills  and  hollows  characteristic  of  drift 
topography.  In  the  river  channel,  however,  stretches  of  dead  water  are 
interspersed  between  rapids  and  falls  in  the  manner  described  as  charac- 
teristic of  the  channel  tln-ougli  the  Quinnesec  schists  of  the  southern  area. 
tSniooth  water  is  more  common  than  in  the  southern  area,  and  rapids  are  less 
common,  probably  partly  because  of  the  thicker  covering  of  drift,  and 
partly  because  of  the  fact  that  the  rocks  are  more  uniform  in  character 
than  in  the  southern  district.  The  Upper  and  the  Lower  Twin  Falls, 
situated  in  sec.  12,  T.  40  N.,  R.  31  W.,  are  about  one-half  mile  apart.  Each 
is  a  single  cascade,  with  a  plunge  of  about  20  feet  (PI.  XII,  B).  Between 
them  is  a  stretch  of  quiet  water  (see  PI.  XII,  A)  flowing  gently  for  the 
most  of  this  distance  between  banks  of  gravel,  sand,  and  clay.  Below 
the  Lower  Twin  Falls  the  stream  is  fairly  rapid,  but  its  banks  are  free 
from  exposures  for  a  distance  of  about  a  mile.  Here  the  river  leaves  the 
schist  area  at  a  little  falls  and  rapids  known  as  the  Fourfoot  Falls.  The 
final  plunge  is  not  above  1  or  2  feet  in  height,  but  back  of  this  the  stream 
flows  over  a  rapids  for  a  distance  of  100  yards  or  more,  and  in  this  distance 
it  makes  a  fall  of  about  6  feet. 

LITHOLOGT. 

The  rocks  of  this  area  are  grayish  green  in  color,  and  so  fine  grained 
that  in  manv  instances  no  texture  can  be  discovered  in  their  hand  specimens. 
Most  of  them  are  schistose,  but  their  schistosity  is  not  particularly  noticeable 
until  an  attempt  is  made  to  break  them,  when  they  tend  to  split  easily  along 
approximately  parallel  planes  like  slates,  and  only  with  difficulty  can  they 
be  made  to  break  in  any  other  direction.  In  some  instances,  however,  the 
schistosity  is  so  perfect  that  the  rocks  cleave  exactly  like  slates.  On  many 
of  the  exposures,  especially  of  the  more  massive  phases,  a  typical  ellip- 
soidal structure  is  discernible.  The  ellipsoids  vary  in  diameter  from  a  few 
inches  to  3  or  4  feet.  There  is  no  sti-iking  contrast  between  the  material 
of  the  ellipsoids  and  that  of  the  matrix  between  them.  In  both  cases  the 
rock  is  a  dense  grayish  greenstone  without  any  distinct  textural  features 
The  matrix  is  usually  slightly  more  schistose  than  the  ellipsoids,  but  other- 
wise it  is  like  them. 

In  a  few  exposures  in  the  northern  and  eastern  poi-tions  of  the  area 
the  rock  is  a  little  coarser  grained.     It  possesses  a  structure  that  suggests 


U.   S.   GEOLOGtCAL    SURVEY 


MONOGRAPH 


A.     BASIN    BELOW    UPPER  TWIN    FALLS. 

The  water  surface  is  smooth  and  the  current  sluggish,     The  rocks  are  dense,  fine-grained,  and  ellipsoidal  greenstones.     The  bridge  is  on  the 

highway  between  Iron  Mountain  and  Florence,  Wis. 


B.      BARRIER    ROCK    AT    UPPER    TWIN    FALLS, 

The  basin  below  the  falls  into  which  the  water  plunges  is  about  20  feet  below  the  crest  of  the  cascade.     The  rock  is  a  dense, 

jointed  greenstone. 


ARCHEAN,  QUINNESEC  SCHISTS.  161 

the  diabasic  structure.  It  is,  moreover,  distinctly  schistose,  but  its  schistosity 
is  more  hke  that  of  the  gneisses  than  Hke  that  of  the  shites.  The  rock 
probably  represents  a  dike  or  a  series  of  dikes  in  the  fine-grained  green- 
stone. At  the  Fourfoot  Falls  the  exposures  consist  of  alternating  bands 
of  massive,  schistose,  and  slaty  rocks  striking  about  N.  80°  W.,  almost  at 
right  angles  to  the  course  of  the  river,  and  yet  these  exposures  are  usually 
schistose  on  the  Wisconsin  side  of  the  stream  and  massive  on  the  Michigan 
side.  At  many  jjlaces,  both  at  this  point  and  elsewhere  in  the  area,  the 
more  massive  phases  alternate  with  schistose  phases  in  the  same  manner  as 
in  the  southern  area.  The  schists  grade  into  the  massive  rocks,  and  often 
no  break  of  any  kind  can  be  discovered  between  them.  This  relation 
suggests  the  origin  of  tlie  former  from  the  latter.  One  peculiar  rock  of 
the  Upper  Twin  Falls  remains  to  be  mentioned.  It  is  observed  in  the 
smooth  face  of  the  exposure  extending  a  little  south  of  east  from  the 
barrier  OA^er  which  the  water  plunges.  It  is  apparently  a  bed  of  con- 
glomerate or  breccia  in  the  schists.  At  its  extreme  eastern  end,  where  first 
met  with,  it  is  a  band  6  feet  wide  composed  of  irregularly  shaped  and  sharp- 
edged  fragments  of  an  aphanitic  green  rock  in  a  matrix  composed  of  small 
angular  fragments  of  chlorite-schist  cemented  together  by  a  mixture  of 
quartz,  calcite,  and  chlorite  (PL  XIII,  ^-1).  The  large  fragments  often 
match  together  in  such  a  way  as  to  indicate  clearly  that  they  were 
originally  portions  of  the  same  mass.  This  was  crushed  into  fragments 
and  these  were  thrust  apart,  and  at  the  same  time  the  matrix  was  forced 
between  them.  To  the  west  this  bed  splits  up  into  several  smaller  ones, 
the  largest  of  which  passes  over  the  brink  of  the  falls.  This  peculiar 
conglomerate  or  breccia  band  strikes  approximately  parallel  to  the  schis- 
tosity of  the  rocks  in  its  vicinity.  It  appears  to  be  a  breccia  zone,  produced 
in  all  probability  by  the  crushing  of  the  rocks  wliich  it  traverses. 

Unlike  the  schists  in  the  Menominee  River,  those  of  the  western  area 
are  rarely  cut  by  dikes.  A  few  intrusions  of  diabase  are  met  with  in  the 
area,  but  granitic  intrusives  are  entirel}'  absent. 

The  microsco])ical  features  of  most  of  the  finer-grained  rocks  of  this 
area  do  not  afford  much  evidence  as  to  their  original  character.  Tie 
rocks  have  suffered  so  much  alteration  that  in  many  cases  all  traces  of 
the  original  structuies  by  which  their  nature  might  have  been  identified 
have  disappeared.     The   composition  of  the  alteration  products,  however, 

MON  XLVI — 04: 11 


162  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

and  the  gradation  of  the  dense  rocks  into  coarser-grained  varieties  which 
still  possess  traces  of  structure,  admit  of  no  interpretation  other  than  that 
the  original  rocks  were  basic  igneous  i-ocks.  Their  fine  grain  and  ellip- 
soidal structure  proclaim  them  lavas. 

Fine-granted  greenstones  and  their  derived  schists. — A  few  of  the  fine- 
grained greenstones  still  retain  their  original  structure,  and  this  is  in  accord 
with  the  character  ascribed  to  them  above.  One  of  the  more  massive 
homogeneous  light-green  rocks  from  the  Fourfoot  Falls  is  described  by 
Williams  as  follows: 

Mineralogically  there  is  hardly  a  trace  of  the  original  rock  left.  Almost 
colorless  hornblende,  pale-green  chlorite,  zoisite,  leucoxene,  and  a  little  calcite  (all  of 
seeondarj'  origin)  are  the  present  constituents;  and  yet  the  original  structui'e  of  the 
rock  is  strikingl}^  well  preserved.  When  viewed  with  a  comparatively  low  power, 
in  ordinarv  light,  the  outlines  of  long,  almost  acicular,  feldspar  crj'stals  are  very 
apparent,  in  spite  of  the  fact  that  the  substance  of  the  feldspar  itself  is  changed  to 
chlorite  or  zoisite.  These  outlines  of  former  cr3^stals  make  a  confused  aggregate, 
but  each  individual  preserves  its  own  proper  form  (idiomorphic  in  the  sense  of  Rosen- 
busch).  The  angular  spaces  between  the  feldspars  produce  a  typical  example  of  the 
ophitic  or  diabase  structure,  although  no  trace  of  a  diabase  mineral  remains." 

This  rock  is  traversed  by  "schistose  bands,  which  show  indications  of 
having  been  much  crushed  and  rubbed.  Slickensides  are  abundant,  and 
lenticular  fragments  fit  into  one  another  so  as  to  produce  an  imperfect  sort 
of  foliation."  Under  the  microscope  this  schistose  rock  exhibits  the  effects 
of  arreat  mechanical  stresses. 


tj"^ 


Curving  and  interlacing  areas  of  pale-green  chlorite  and  of  a  grayish  substance 
(pei'haps  the  remains  of  titanic  iron)  form  the  main  mass  of  this  rock.  Thickh'  scat- 
tered through  these  are  patches  of  a  dark-brown  substance,  often  showing  concentric 
zones  of  a  clear,  transparent  character.  These  look  like  opal,  but  their  optical  character 
shows  them  to  be  single  individuals  of  crystalline  quartz.  Imbedded  in  this  material 
of  such  pronounced  secondary  character  are  fragments  of  feldspar,  which  have  been 
crushed  or  broken.  These  *  *  *  are  less  changed  chemically  than  those  in  the 
massive  rock  from  which  this  schistose  band  has  been  derived.* 

Other  schists  of  this  vicinity  are  composed  of  hornblende,  chlorite, 
feldspar,  quartz,  and  leucoxene.  Most  of  the  hornblende  is  a  pale-green 
variety,  surrounding  compact  cores  of  a  brown  variety  of  the  same  mineral, 
from  which  the  lighter-colored  phase  is  believed  to  have  been  derived  by 

aWilliams,  op.  cit.,  pp.  124-125.  ^Ibid.,  p.  125. 


u.   «.   r.EOLnr.irAi.    curve' 


A.     BRECCIATED    BAND   OF   MASSIVE   FINE-GRAINED   GREENSTONE  AT   UPPER   TWIN    FALLS. 

The  fragments  are  mainly  dense,  I'ght-coloied  greenstone.     The  matrix  is  a  schistose,  chloritized  greenstone  containing 

streaks  of  chlorite, 


Ji      RIDGE   OF    DOLOMITE  SOUTH    OF    LAKE   ANTOINE. 

One  of  the  typical  hills  of  the  dolomite  formation.     View  taken  from  north  side  of  the  Clifford  open  pit,  Traders  mine.      The  crest  of  the  hil 

is  about  two  miles  south. 


ARCHEAN,  QUINNESEC  SCHISTS.  163 

bleaching.  In  these  rocks  no  diabasic  texture  was  observed.  This  fact, 
together  with  the  presence  of  the  brown  hornblende,  seems  to  indicate  that 
the  original  rock  from  which  the  schist  was  derived  may  have  been  a 
diorite. 

At  the  Twin  Falls  the  rocks  are  so  much  altered  that  no  trace  of  their 
original  structure  can  be  detected.  They  are  usually  dense,  homogeneous, 
dark-green  rocks,  composed  of  a  confused  aggregate  of  pale-green  fibrous 
hornblende,  shreds  of  biotite,  remnants  of  plagioclase,  and  grains  of  ilmenite. 
Around  the  feldspar  remnants,  and  occupying  the  space  originally  occupied 
by  this  mineral,  is  now  a  mass  of  actinolite,  zoisite,  and  epidote. 

These  rocks  are  crossed  by  bands  of  chlorite-schists,  consisting  of 
bright-green  chlorite,  finely  granular  quartz,  and  perhaps  some  secondary 
albite.  In  addition  to  these  components  the  schists  also  often  contain 
grains  of  ilmenite  and  leucoxene,  flakes  of  biotite,  and  occasionally  crystals 
of  tourmaline. 

The  contacts  between  the  schists  and  the  massive  phases  are  often 
very  indefinite.  The  rocks  grade  into  each  other  by  infinitesimal  variations. 
As  described  by  Williams,"  the  first  step  in  the  production  of  the  schistose 
structure  is  the  division  of  the  massive  rock  by  two  systems  of  joints  inter- 
secting at  acute  angles.  These  joints  divide  the  mass  into  rhomboidal 
prisms,  whose  cross  sections  are  well  displayed  on  the  smooth  glaciated 
surfaces  of  many  of  the  ledges.  As  the  schistose  phases  of  the  rock  are 
approached,  the  joints  become  more  and  more  nearly  parallel,  with  tlie 
result  that  the  rhombs  are  all  lengthened  in  a  corresponding  direction. 
The  elongated  prisms  finally,  by  a  more  severe  action  of  the  lengthening 
process,  become  very  thin  and  much  extended  lenses,  which  produce 
a  well-developed  wavy  schistosity.  The  process  is  plainly  dynamic,  the 
schistosity  being  produced  by  pressure  acting  at  right  angles  to  the  final 
direction  of  the  foliation. 

Coarse-grained  greenstones  and  their  derived  schists. — Although  most  of 
the  rocks  in  the  western  Quinnesec  schist  area  are  of  the  indeterminable 
character  described  above,  a  few  of  them  possess  more  definite  characteris- 
tics. A  few  exposures  are  plainly  porphyritic.  The  phenociysts  were 
originally  plagioclase,  and  the  groundmass  was  a  fine-grained  ophitic  aggre- 
gate that  may  have  contained  some  glass.     These  rocks  must  be   classed 

"Williams,  op.  cit.,  p.  128-129. 


164  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

with  the  basalts.  Their  relations  to  the  fine-grained  homogeneous  green- 
stones can  not  be  seen,  so  that  it  can  not  be  determined  whether  they  are 
dikes  or  flows. 

In  a  few  instances  coarser-grained  rocks  have  retained  enough  of  their 
original  structure  to  leave  no  doubt  as  to  their  character.  Of  course  they 
are  much  altered,  but  they  show  plainly  the  divergent  radial  structure  of 
diabases.  Moreover,  some  of  them  still  possess  remnants  of  augite  grains, 
surrounded  by  light-green  hoi-nblende  in  the  triangular  areas  between  the 
plagioclase  laths.  Through  the  hornblende  are  scattered  little  grains  of 
magnetite,  ilmenite,  leucoxene,  a  few  crystals  of  rutile,  and  nests  of  calcite. 
The  plagioclase  is  partly  fresh,  partly  changed  to  zoisite,  and  partly  changed 
to  chlorite. 

These  rocks  are  nearly  massive,  only  traces  of  foliation  being  occasion- 
ally observed  in  them.  Their  constituents  are  much  fresher  than  those  of 
the  schists  aiid  the  dense  greenstones.  Although  their  relations  to  the  lat- 
ter rocks  can  not  be  seen  it  is  probable  that  they  are  younger  than  these, 
and  that  they  are  dike  masses  intruding  them. 

Fragmental  schists. — The  only  rocks  in  the  area  that  appeal-  to  l)e  frag- 
inental  are  several  narrow  bands  at  the  Upper  Twin  Falls,  just  below  the  Cas- 
cade. The  bands  are  only  an  inch  or  two  in  width.  In  the  field  they  were 
supposed  to  be  stringers  from  the  breccia  already  referred  to  (p.  1 61)  as  occur- 
ring at  this  place.  Under  the  microscope  the  rock  is  seen  to  be  very  differ- 
ent from  anything  else  found  among  the  western  Quinnesec  schists.  It  is 
plainly  a  very  fine-grained  aggregate  of  quartz  and  tiny  grains  and  specks 
of  some  black,  opaque  substance.  From  the  fact  that  the  bands  run  irreg- 
ularly through  the  greenstones,  it  is  believed  that  they  represent  cracks 
that  were  filled  from  above  by  material  from  some  of  the  Huronian  beds 
that  must  once  have  overspread  the  greenstones. 

A  somewhat  similar  rock  is  described  by  Williams  from  the  same  place. 
It  constitutes  one  of  the  schist  bands  alternating  with  the  more  massive 
greenstones.     The  thin  section — 

contains  irregular  and  angular  fragments  of  quartz  and  a  slightly  altered  feldspar  of 
considerable  size.  These  are  imbedded  in  a  matrix  of  irregular  grain,  composed  of 
chlorite,  calcite,  quartz,  and  opaque  iron  oxide,  which  is  accompanied  by  leucoxene. 
The  chlorite  scales  often  have  a  radially  divergent  arrangement  around  the  larger 
included  fragments  of  quartz  and  feldspar." 

"Williams,  op.  cit.,  p.  133. 


ARCHEAN,  QUINNESEC  SCHISTS.  165 

The  particular  schist  band  from  which  this  specimen  was  taken  differs 
from  most  of  the  schists  of  the  area  in  the  fact  that  its  contact  with  the 
massive  rocks  is  very  sharp  and  distinct.  This  leads  Williams  to  the  con- 
clusion that  it  is  not  simply  a  schistose  phase  of  the  massive  rock,  but  that 
it  represents  a  distinct  bed  in  a  volcanic  series,  the  massive  rocks  and  the 
schists  derived  from  them  being  old  lava  flows  and  the  schist  just  described 
being  a  tuff  bed. 

ORIGIN    OF   THE    KOCKS. 

The  fine-grained  texture  of  most  of  the  rocks  of  tlie  western  area  of 
Quinnesec  schists,  when  considered  in  connection  with  their  composition, 
indicates  that  they  are  old  lava  flows  of  the  general  character  of  basalts. 
Their  ellipsoidal  structure  points  to  the  same  conclusion.  In  the  Crystal 
Falls  district,  a  few  miles  west  of  the  Menominee  district,  the  greenstones 
associated  with  the  Huronian  deposits  exhibit  this  structure  in  a  peculiarly 
fine  manner.  These  rocks  are  plainly  volcanic  flows,  since  they  occur  in  well- 
defined  beds,  many  of  which  are  amygdaloidal.  The  Quinnesec  schists 
seem  to  have  originated  in  the  same  kinds  of  rocks.  They  have,  however, 
suffered  so  much  more  metamorphism  than  the  Crystal  Falls  volcanics  that 
their  distinctive  volcanic  characteristics  have  disappeared." 

Tuff  beds  may  have  been  associated  with  the  old  lava  flows,  but  if  so, 
they  seem  to  have  been  in  very  subordinate  quantity.  At  any  rate,  there 
is  no  certain  evidence  that  they  ever  exisited  in  the  area,  though  they  may 
have  done  so. 

The  volcanic  beds  were  cut  by  basic  intrusions,  and  then  the  whole 
complex  was  folded.  Where  the  folding  was  severe  the  finer-grained  lavas 
and  tuffs  were  changed  into  fissile  schists,  and  the  coarse-grained  beds  into 
schistose  greenstones.  Where  the  folding  was  less  severe  all  the  rocks  were 
rendered  schistose,  but  the  resulting  schists  still  retained  traces  of  their 
original  structures.  After  the  folding  other  basic  intrusions  took  place. 
These  are  represented  by  a  few  massive  diabases  met  with  in  the  area. 

INTERESTING    LOCALITIES. 

The  best  exposures  of  the  rocks  of  this  area  are  found  at  the  Twin 
Falls  and  the  Fourfoot  Falls.  Both  the  Twin  Falls  are  easily  reached  by 
the  wagon  road  from  Iron  Mountain  to  Florence,  Wis.     The  two  falls  are 

o  Clements,  J.  M.,  Mon.  U.  S.  Geol.  Survey,  vol.  36,  1899,  pp.  113-135. 


166  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

about  half  a  mile  apart,  but  it  is  only  in  the  vicinity  of  the  cascades  that 
rock  exposures  are  abundant. 

Upper  Twin  Falls.— At  the  Upper  Twin  Falls  (PI.  XII,  A  and  B), 
low  flat  exposures  occur  practically  all  the  way  from  the  highway  bridge 
around  the  basin  below  the  falls  to  a  point  a  little  above  the  cascade. 
The  ledges  here  are  fine  examples  of  the  dense,  dark-  colored  massive  green- 
stones exhibiting  the  ellipsoidal  structure.  This  structure  is  best  seen  on 
the  flat  rocks  near  the  water's  edge  on  the  Michigan  side  of  the  river  just 
above  the  bridge.  The  rock  is  dense  and  presents  a  smooth,  almost 
featureless  surface.  On  it,  however,  by  close  inspection,  can  be  detected 
round  and  oval  areas  separated  from  interstitial  areas  by  fine  lines.  The 
rock  within  the  lines  and  that  without  them  is  practially  alike,  except  that 
the  former  is  sometimes  slightly  different  in  tinge  from  the  lattei*.  The 
round  and  oval  areas  are  cross  sections  of  ellipsoids  which,  in  this  ledge, 
vary  in  size  from  those  having  a  diameter  of  6  or  7  inches  to  those  having 
a  similar  dimension  of  a  little  over  2  feet.  None  of  them  have  amygdaloidal 
peripheries. 

Near  the  falls,  on  both  sides  of  the  river,  and  at  the  lower  end  of  the 
basin  below  the  falls,  on  the  Wisconsin  side,  several  bands  of  chlorite-schist 
traverse  the  massive  rocks,  but  they  are  rare.  At  the  cascade,  and  on  its 
east  side,  is  the  narrow  band  of  fragmental  greenstone  referred  to  in  a 
previous  page  (p.  161). 

Lower  Twin  Falls. — At  the  Lower  Twin  Falls  the  ledges  are  larger  and 
rougher  than  at  the  more  northerly  fall.  The  rocks  are  practically  the 
same  at  both  places,  but  at  the  lower  falls  the  schistose  phases  are  rather 
more  common.  Here  can  be  well  seen  the  transition  between  the  massive- 
jointed  greenstones  and  the  chlorite-schists,  and  here  also,  on  a  small  scale, 
can  be  seen  the  actual  passage  of  massive  into  schistose  phases  along  shear- 
ing zones.  Just  below  the  falls,  on  the  Michigan  side,  the  dense  rock  is 
traversed  by  a  seam  of  quartz  occupjnng  a  crack  along  which  there  has 
been  movement.  The  rock,  at  the  distance  of  a  few  inches  from  the  vein, 
is  quite  massive;  nearer  the  vein  it  becomes  schistose,  with  a  foliation 
inclined  about  45°  to  the  direction  of  the  vein,  and  very  near  the  vein  it  is 
a  typical  chlorite-schist.  Similar  chlorite-schists  may  also  be  seen  in  this 
ledge  coating  surfaces  of  joint  planes. 

Fourfoot  Falls. — At  the  Fourfoot  Falls  the  rocks  exhibit  greater  ^-ariety. 


ARCHEAN,  NORTHERN  COMPLEX.  167 

The  falls  themselves  are  not  much  more  than  a  rapids  over  ledges  of 
greenstone-schists.  The  Chicago  and  Northwestern  Eailway  bridge,  on 
the  line  between  Iron  Mountain  and  Commonwealth,  crosses  the  river  at 
the  foot  of  the  rapids.  For  a  few  hundred  yards  above  the  bridge  instructive 
exposures  can  be  seen  on  both  sides  of  the  stream.  Alternating  bands  of 
massive  and  schistose  greenstones,  'striking  about  N.  80°  W.,  outcrop  on 
bare  banks  and  form  the  rapids  and  several  small  islands  in  the  river.  On 
the  Michigan  side  the  prevailing  rocks  are  massive.  On  the  Wisconsin  side 
schists  predominate. 

At  the  western  end  ot  tlie  railroad  bridge  the  rock  is  a  light-green 
ajDhanitic,  massive  greenstone,  traversed  here  and  there  by  wavy  bands  of 
schistose  greenstone,  characterized  by  abundant  slickensides.  Beyond  this 
to  the  north  is  a  narrow  band  of  a  black  graphitic-looking  schist,  and  north 
of  this  another  band  of  schistose  greenstone  best  exposed  near  the  water's 
edge.  Immediately  north  of  this  exposure  rises  a  high,  sheer  cliff,  under- 
mined at  the  base  by  hollows  produced  artificially.  This  consists  of  a  soft, 
black,  slaty-looking,  very  schistose,  and  quite  fissile  rock.  In  the  hand 
specimen  and  in  the  ledge  it  bears  a  strong  resemblance  to  a  black  slate, 
but  under  the  microscope  it  is  seen  to  be  a  chlorite-schist.  At  the  water's 
edge,  beyond  the  cliif,  the  schist  again  appears,  and  north  of  this  follow 
ledges  of  schistose  greenstone. 

On  the  Michigan  side  the  rock  is  fairly  imiform  in  character.  The 
southernmost  ledge  just  under  the  bridge  is  a  massive,  dense,  light-green 
rock.  The  northernmost  ledge  is  a  dark  greenstone-schist.  The  intervening 
low  ledges  that  dot  the  bank  are  massive  and  schistose  greenstones  that  are 
a  little  coarser  in  grain  than  the  rock  under  the  bridge.  In  the  rocks  of 
some  of  these  ledges  the  diabasic  structure  is  plainly  discernable,  but  in 
most  ledges  the  grain  is  so  fine  that  no  well -characterized  structure  is 
observable  except  in  thin  section  under  the  nucroscope. 

SECTION   2.  NORTHERN   COMPIiEX. 

The  rocks  constituting  the  Northern  Complex  are  gneissoid  granites, 
banded  gneisses,  hornblende-schists,  and  a  few  feldspathic  green  schists, 
identical  with  some  of  the  squeezed  basic  schists  among  the  Quinnesec 
schists.  Mica-schists  also  occur  in  the  complex,  but  they  are  rare.  They 
have  been  found  only  in  a  few  exposures  in  the  interior  of  the  Archean  area 


168  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

north  of  the  limits  of  the  map.  The  granites,  gneisses,  and  schists  are  cut 
by  dikes  of  coarse-grained  and  fine-grained  basic  rocks,  by  small  dikes  and 
veins  of  aplite  and  pegmatite,  and  by  numerous  quartz  veins. 

DISTRIBUTION. 

These  rocks  occupy  an  elliptical  area  north  of  the  Menominee  trough 
of  fragmentals,  separating  it  from  thj  Calumet  trough  farther  north.  The 
complex  is  separated  from  the  Huronian  beds  by  unconformities  and  by 
basal  conglomerates  which  will  be  referred  to  later.  Onlj^  those  rocks 
occurring  along  the  southern  edge  of  the  area  have  been  studied  in  detail. 
The  rest  of  the  area  has  been  examined  sufficiently  closely,  however,  to 
warrant  the  statement  that  it  does  not  diifer  in  any  essential  respect  from  its 
sovithern  periphery. 

TOPOGRAPHT. 

The  topography  of  the  country  underlain  by  the  crystalline  rocks  is 
not  unlike  that  of  Basement  Complex  areas  elsewhere.  In  the  western 
portion  of  the  area  small  and  large,  rounded,  glaciated  hummocks  of  rock, 
often  with  precipitous  sides  to  the  south,  rise  above  the  gravels  and  sands 
of  the  glacial  deposits.  In  the  eastern  part  of  the  district,  where  these 
deposits  are  thinner,  the  hills  protrude  higher  above  the  drift,  appearing  as 
groups  of  knolls  with  bare,  fairly  smooth  upper  surfaces,  but  with  ragged 
and  precipitous  sides. 

SEQUENCE    OF    ROCKS. 

The  study  of  the  relations  of  the  rocks  of  the  complex  to  one  another 
has  not  aftbrded  any  more  data  for  determining  their  exact  sequence  than 
studies  in  other  Archean  areas.  In  general  it  appears  that  some  of  the 
gneisses  and  some  of  the  hornblende-schists  are  older  than  most  of  the 
granites.  Others  of  the  schists  are  plainly  mashed  intrusives  that  are 
younger  than  most  of  the  granites.  All  of  the  greenstone-schists  are  of 
this  nature.  The  aplites,  pegmatites,  and  some  of  the  basic  intrusives 
are  the  youngest  rocks  belonging  in  the  complex,  but  even  these,  since 
they  are  not  known  to  cut  through  the  Huronian  beds,  are  thought  to 
have  taken  their  present  position  before  the  sediments  were  deposited.  The 
latest  of  all  the  intrusives  are  certain  coarse-grained  massive  diabases  and 
gabbros.  These  rocks  not  only  occur  as  intrusives  in  the  complex,  but 
they  are  foimd  also  in  the  lower  member  of  the  Hui'onian  series  overlying 


ARCHEAN,  NORTHERN  COMPLEX.  169 

the  Arcliean  rocks.  There  is  no  reason  to  believe  that  any  of  the  rocks  of 
the  complex  are  metamorphosed  sediments.  Most  of  them  are  clearly 
igneous  in  origin. 

LITHOLOGT. 

GNEISSOID   GRANITES. 

The  most  abundant  rocks  of  the  complex  are  gneissoid  granites  and 
granitic  gneisses.  These  rocks  differ  from  one  another  in  no  essential 
respect.  The  former  are  merely  less  schistose  than  the  latter.  Both 
embrace  a  series  of  medium-grained  to  fine-grained  gi'ay  and  jjink  rocks 
with  a  granitic  texture  that  sometimes  approaches  in  appearance  the  texture 
of  fine-grained  quartzites.  The  pink  or  red  granites  are  usually  a  little 
coarser  grained  than  the  gray  ones.  In  the  hand  specimen  red  orthoclase 
is  seen  to  be  the  principal  constituent.  In  addition  to  this  there  can  also  be 
detected  a  few  grains  of  white  feldspar,  a  large  number  of  quartz  grains, 
and  an  occasional  flake  of  mica.  The  gray  granites  appear  to  be  almost 
homogeneous.  Here  and  there  through  them  are  stringers  and  patches  of 
pink  granite,  but  most  of  the  hand  specimens  are  of  a  nearly  uniform  dark- 
gray  tint.  The  gray  rock  passes  into  the  pink  rock  by  almost  impercep- 
tible stages,  the  differences  in  the  tints  of  the  two  end  members  of  the 
gradation  series  being  due  mainly  to  the  color  of  their  feldspathic  component. 

In  some  instances  the  pink  stringers  are  very  coarse-grained  aggregates 
of  feldspar  and  quartz,  like  pegmatites.  The  material  of  these  pegmatitic 
veins,  like  that  of  the  finer-grained  ones,  grades  into  the  mass  of  the  gray 
rock.  There  is  nowhere  any  sharp  contact  between  the  two.  The  red 
granite  does  not  seem  to  be  of  the  nature  of  an  ordinary  intrusive,  but  it 
appears  rather  to  have  the  character  of  an  impregnation,  which  saturated  the 
gray  granite  and  crystallized  in  certain  places  as  patches  or  in'egularly  shaped 
stringers,  and  in  other  places,  probably  along  cleavage  planes,  as  more 
regular  and  definite  veins.  In  the  banded  gneisses,  to  be  referred  to  later, 
the  pegmatitization  followed  approximately  parallel  planes,  but  in  the  gray 
and  pink  gneissoid  granites  it  took  place  irregularly  through  the  rock  mass. 

Under  the  microscope  all  the  granites  and  granitoid  gneisses  of  this 
area,  whether  of  the  pink  or  the  gray  variety,  are  found  to  consist  of  quartz, 
orthoclase,  plagioclase,  and  biotite,  and  large  quantities  of  the  decomposition 
products  of  the  last-named  mineral,  and  of  the  feldspars.  The  most  abundant 
of  the  decomposition  products  are  kaolin  and  chlorite,  but  sericite,  calcite. 


170  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

epidote,  and  ocher  are  nearly  always  present  in  small  qnantity.  Rutile, 
zircon,  and  apatite  are  also  present  as  accessories.  In  some  sections  a  little 
microcline  is  also  to  be  found  among  the  feldspars.  It  appears  in  all  cases 
to  be  an  original  component  and  not  a  new  product  as  in  the  Marquette 
granites. 

All  the  feldspars  are  altei'ed.  Small  flakes  of  sericite  and  spicules  of 
kaolin  are  scattered  through  them  somewhat  uniformly.  The  microcline  and 
the  plagioclase  have  undergone  less  alteration  than  the  orthoclase,  which  in 
many  sections  is  so  completely  decomposed  that  no  trace  of  the  original 
material  can  now  be  detected. 

The  biotite  is  a  green  variety  with  a  pleoehroism  in  yellowish -green 
and  emerald-green  tints.  It  is  present  as  small  flakes  and  in  aggregate  of 
flakes  between  the  feldspars  and  the  quartz.  The  secondary  chlorite  and 
epidote  are  found  mainly  in  the  vicinity  of  the  biotite,  from  which  they  seem 
to  have  been  derived.  At  all  events,  when  these  products  are  abundant  the 
biotite  appears  to  be  more  or  less  bleached. 

The  red  granites  differ  from  the  gray  varieties  mainly  in  tlie  fact  that 
the  feldspars  of  the  former  inclose  large  numbers  of  inclusions  of  hematite 
and  reddish-brown  ocher.  They  also  contain  but  little  biotite  and  almost 
no  microcline.  In  other  respects  the  two  rocks  are  essentially  the  same. 
The  red  granite  appears  to  be  a  little  more  decomposed  than  the  gray  rock 
and  is  apparently  more  crushed,  but  otherwise  there  is  little  besides  difference 
in  color  to  distinguish  the  two. 

All  specimens  of  the  gneissoid  granites  show  plainly  the  eftects  of 
mashing.  Many  of  their  components  are  broken  and  squeezed  out  into 
lenticular  masses,  which  give  the  rocks  their  schistosity.  The  peripheral 
portions  of  many  of  the  grains  are  granulated  and  in  these  granulated 
portions  is  found  the  greater  portion  of  the  secondary  sericite. 

BANDED   GNEISSES. 

The  banded  gneisses  are  composed  of  the  same  components  as  are  the 
gneissoid  granites.  Secondary  products  are,  however,  more  abundant  than 
in  the  granites,  and  the  primary  constituents  are  usually  less  fresh  looking. 
At  fii-st  glance  these  banded  gneisses  appear  to  be  made  up  of  alternate 
parallel  bands  of  gray  and  pink  schistose  granitic  material  like  that  of  the 
gray  and  pink  gneissoid  granite  described  above.  A  close  inspection  of 
the  ledges,  however,  shows  that    while    these    bands    are    approximately 


ARCHEAN,  NORTHERN  COMPLEX.  171 

parallel  for  short  distances,  they  nevertheless  wedge  out  when  traced  for 
distances  of  18  or  24  inches,  split  up  into  several  narrower  bands,  or 
coalesce  with  other  bands,  forming  broader  ones.  Often,  also,  narrow 
bands  of  one  color  cut  across  broader  bands  of  the  other  color,  so  that  the 
rocks  are  actually  made  up  of  an  interlacing  network  of  veins  with  meshes 
of  very  unequal  dimension.  The  long  dimensions  are  parallel  to  the 
apparent  banding  of  the  rocks,  which  is  also  the  direction  of  their 
schistosity,  and  the  short  dimensions  are  perpendicular  thereto. 

The  banded  gneisses  are  thus  like  the  mottled  red  and  gray  gneissoid 
granites  in  the  fact  that  they  consist  of  granitic  impregnations  in  a  granitic 
rock  The  impregnations  in  the  banded  rock,  however,  followed  approxi- 
mately parallel  courses,  while  in  the  mottled  rocks  they  occun-ed  irregularly. 
The  source  of  the  imjiregnating  material  may  very  well  be  the  rock  in 
which  the  impregnations  took  place.  This  niay  have  been  partially  dis- 
solved, yielding  solutions  which  transported  the  dissolved  material  to  situa- 
tions where  the  conditions  were  favorable  to  its  crystallization. 

HORNBLENDE-SCHISTS. 

The  hornblende-schists  are  usually  lustrous  greenish-black  schists, 
with  the  normal  characteristics  of  such  rocks.  They  are  cut  by  the  gran- 
ites in  some  places.  In  other  places  large  blocks  are  found  included  in 
granite.  Plainly  they  are  older  than  the  granites,  and  probably  they  are 
the  oldest  rocks  in  the  northern  complex.  A  second  kind  of  hornblendic 
schist  exists  in  which  the  rocks  are  so  related  to  the  g]-anites  and  gneisses 
that  they  must  be  regarded  as  dikes.  In  some  places  they  appear  as  bands 
cutting  across  the  banding  of  the  gneisses,  and  in  others  as  bands  conform- 
ing in  strike  and  dip  with  the  lighter-colored  bands  of  these  rocks.  These 
schists  are  therefore  looked  upon  as  mashed  intrusives.  They  differ  from 
the  schists  of  the  first  kind  in  being  duller  in  luster  and  in  having-  a  greener 
tinge. 

In  their  petrographical  character  the  hornblende-schists  vary  between 
normal  phases  composed  of  hornblende,  quartz,  epidote,  and  perhaps  occa- 
sionally a  little  feldspar,  and  greenstone-schists  composed  of  amphibole, 
plagioclase  and  its  decomposition  products,  quartz,  epidote,  kaolin,  calcite, 
and  sericite.  As  the  proportion  of  quartz  present  increases,  sericite,  calcite, 
and  kaolin  gradually  disappear,  and  the  rocks  approach  more  and  more 
nearly  the  normal  hornblende-schists  in  appearance  and  composition.     This 


172  THE  MENOMINEE  IRON  BEARING  DISTRICT. 

gradation  from  rocks  that  are  unquestionably  altered  basic  rocks  to  true 
hornbleude-scliists  maj"  not  often  be  observed  in  a  single  outcrop,  but  the 
two  end  members  of  the  series  are  united  by  so  many  gradational  phases 
that  there  can  be  little  question  that  they  are  genetically  connected.  It  is 
very  evident  from  the  microscopical  study  of  their  thin  sections  that  the 
feldspathic  hornblende-schists  are  squeezed  and  altered  basic  eruptives. 
It  is  very  probable  that  the  nonfeldspathic  hornblende-schists  have  the 
same  origin  and  that  they  dift'er  from  the  feldspathic  schists  only  in  the 
amount  of  masliing  to  which  they  have  been  subjected  and  the  consequent 
amount  of  alteration  they  have  suffered. 

INTKUSIVES. 

The  granites,  gneisses,  and  schists  are  cut  by  veins  of  granite,  pegma- 
tite, aplite,  and  quartz,  and  by  well-defined  dikes  of  basic  rocks. 

Acid  intrusives. — The  granite  veins  are  of  all  sizes,  from  a  few  feet  to  a 
few  inches  in  width.  Their  material  is  identical  with  that  of  the  red 
granites  refeiTed  to  a  few  pages  back. 

The  pegmatites  are  coarse-grained  red  rocks  composed  of  red  ortho- 
clases  and  white  quartz.  The  feldspar  is  in  grains  that  occasionally  have 
rudely  outlined  crystal  forms  and  the  quartz  in  irregular  areas  between 
these.  While  the  rock  bears  some  resemblance  to  a  graphic  granite,  the 
peg.natitic  structure  is  not  very  pronounced. 

The  aplite  is  a  fine-grained  purplish  rock,  in  which  can  plainly  be 
seen  small  lath-shaped  crystals  of  red  feldspar  lying  in  a  fine-grained 
matrix  composed  of  irregular  grains  of  red  orthoclase  and  irregular  dark- 
gray  areas  of  a  black  micaceous  mineral  and  white  quartz.  The  rock  is 
quite  massive,  not  the  slightest  evidences  of  schistosity  being  observed  in 
it.  Under  the  microscope  the  latli-shaped  crystals  are  found  to  be  andes- 
ine.  In  addition  to  the  lath-shaped  crystals  there  are  present  also  many 
quadrangular  sections  of  a  feldspar  that  extinguishes  differentl}'  in  the  four 
quadrants.  These  apparently  consist  of  orthoclase  twinned  according  to 
the  Manebach  and  the  Carlsbad  laws.  These  feldspars  are  embedded  in 
a  groundmass  made  up  of  orthoclase,  quartz,  epidote,  green  chlorite,  calcite, 
a  little  brown  biotite,  and  some  rutile. 

The  orthoclase  and  the  quartz  compose  the  greater  part  of  the 
groundmass.  They  are  mainly  in  micropegmatitic  intergrowths,  the  quartz 
apparently  saturating  the  feldspar.     Untwinned  orthoclase  is  also  often  found 


ARCHEAN,  NORTHERN  COMPLEX.  173 

surrounding-  the  quadrangular  feldspar  phenocrysts  above  referred  to,  while 
the  quartz  occupies  the  same  position  with  respect  to  areas  of  micropeg- 
matite  in  which  the  quaitzose  constituent  predominates  over  the  feldspathic 
one.  Between  the  phenocrysts  and  the  areas  of  micropegmatite  is  an  aggre- 
gate of  quartz,  orthoclase,  and  the  other  minerals  mentioned  above.  In 
this  aggregate  quartz  and  feldspar  are  in  small  grains,  the  former  with 
rounded  contours  and  the  latter  with  very  irregular  ones.  The  other 
constituents  are  also  in  the  aggregate,  the  chlorite  as  fairly  large  green 
flakes  that  look  as  thougli  they  may  have  been  derived  from  biotite,  the 
epidote  as  colorless  irregularly  shaped  grains,  the  rutile  as  tiny  crystals, 
and  the  calcite  as  nests  in  the  interstices  between  the  quartz  and  feldspar 
grains. 

The  orthoclase  of  the  phenocrysts  and  also  of  the  groundmass  is  always 
more  or  less  altered  into  kaolin-like  decomposition  products,  the  porphyritic 
cr3^stals,  however,  being  much  less  decomposed  than  the  grains  of  the 
matrix. 

Basic  intrusives. — The  basic  dikes  consist  of  rocks  that  are  known 
comprehensively  as  "greenstones,"  dark-green  rocks  produced  by  the  altera- 
tion of  basalts,  diabases,  or  gabbros.  The  dikes  vary  widely  in  size.  Some 
are  only  a  foot  or  two  in  width,  while  others  measure  as  much  as  300  feet. 
The  smaller  intrusions  are  usuallv  dike-like  in  form,  while  the  larger 
ones  are  more  boss-like  in  chai'acter.  Their  intrusions  follow  the  same 
general  courses  for  short  distances,  but  they  vary  in  width  and  have  ii-regu- 
lar  contacts  with  the  rocks  through  which  they  intrude. 

A  few  of  the  basic  intrusives  may  be  limited  to  the  Basement  Com- 
plex. The  majority  of  them,  however,  cut  both  the  rocks  of  this  series  and 
those  of  the  Huronian.  In  several  instances  the  large  dikes  may  be  traced 
step  by  step  across  the  contact  of  the  granite-schists  series  into  the  quartz- 
ites  of  the  Lower  Huronian  without  any  break  in  their  continuity,  so  that 
in  these  cases  there  is  no  question  but  that  they  are  younger  than  the  quartz- 
ites  of  the  iron-bearing  series. 

The  macroscopic  aspects  of  these  rocks  are  those  of  the  ancient  basic 
dike  rocks  so  common  in  Archean  areas  everywhere.  Some  of  them  are 
fine-grained  green  rocks  without  any  peculiarly  characteristic  structure, 
others  are  darker-colored,  medium-grained  rocks  with  a  distinct  diabasic 
structure,  and  others  are  coarse-grained  varieties  with  a  granular  structure. 


174  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

These  last  mentioned  are  gabbros,  the  others  are  diabases,  some  of  which 
are  very  fresh,  while  many  are  much  altered. 

Under  the  microscope  the  diabases  are  identical  in  every  respect  with 
the  diabases  cutting  the  Quinnesec  schists,  and  the  gabbros  with  corre- 
sponding phases  of  the  basic  intrusives  in  the  Huronian  beds  (see  pp. 
185-186). 

INTERESTING    LOCALITIES. 

The  rocks  of  this  series  are  well  exposed  along  the  entire  northern  side 
of  the  Menominee  trough.  They  may  be  seen  at  almost  any  place  north 
of  the  quartzite  belt  in  a  number  of  small  exposures  separated  from  each 
other  bv  stretches  of  glacial  drift.  The  best  and  largest  exposures  are  in 
sees.  29,  31,  and  32,  T.  41  N.,  R.  29  W.,  and  sees.  1,  2,  and  12,  T.  40  N., 
R.  30  W.,  where  the  rocks  forms  liuge  bare  cliffs  that  are  almost  in  contact 
with  equally  large  cliffs  of  quartzite  (see  PI.  XIV).  These  exposures  are 
easy  of  access  from  Iron  Mountain  by  the  road  that  leads  from  this  city  to 
the  so-called  gold  mine  that  has  been  opened  in  the  quartzite  in  their 
vicinity.  They  present  the  usual  features  characteristic  of  Archean 
complexes. 


CHAPTER  V. 

THE  ALGONKIAN  SYSTEM. 

General  character  and  definition. — The  Algonkiau  rocks  constituting  the 
Menominee  trough,  though  strongh^  metamorphosed,  are  recognized  as 
mainly  sediments.  The  greater  mass  of  tliese  sediments  is  mechanical, 
clastic  textures  usually  being  plainly  apparent  in  them.  The  iron  forma- 
tions are  largely  mechanical,  but  with  tlie  mechanical  material  an  impoi'tant 
amount  of  chemical  and  organic  material  was  deposited,  and  some  of  the 
jaspers  of  the  formation  may  be  wholly  chemical  or  organic.  The 
dolomites  ai"e  principally  chemical  or  organic  sediments,  but  in  their  lower 
portions  thei-e  is  an  abundant  admixture  of  mechanical  debris.  The 
sedimentary  rocks  have  been  intruded  by  a  few  coarse-grained  and  some 
fine-grained  basic  igneous  rocks.     The  latter  are  now  usually  schistose. 

The  lowest  member  of  the  Algonkian  system  has  at  its  bottom  basal 
conglomerates,  which  rest  unconformably  upon  the  Archean  I'ocks  of  the 
Northern  Complex.  These  conglomerates  may  be  seen  at  a  number  of 
places  along  the  north  border  of  the  trough.  Their  best-known  exposures 
are  those  at  the  Falls  of  the  Sturgeon  River,  made  classic  by  Credner, 
Brooks,  and  Irving.  Hence  the  Algonkian  rocks  are  younger  than  the 
underlying  schists. 

The  members  of  the  system  are  likewise  separated  from  the  overlying 
Cambrian  sandstone  by  a  profound  unconformity.  The  Algonkian  rocks 
are  folded;  the  sandstone  is  practically  horizontal.  The  latter  thus  lies 
across  the  truncated  ends  of  the  eroded  folds.  Its  lower  layers  are  formed 
largely  of  the  debris  of  the  more  ancient  rocks.  Hence  the  Algonkian  rocks 
formed  a  land  surface  for  a  vast  period  of  time  before  the  deposition  of  the 
Cambrian  sandstones. 

Unconformity  tvithin  the  system. — Within  the  Algonkian  system  there 
is  an  unconformity  corresponding  to  that  in  the  Marquette  district  between 

175 


176  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  Upper  Marquette  and  the  Lower  ]\Iarquette  series.  This  unconformity 
is  not  so  plainly  marked  in  the  Menominee  as  it  is  in  the  Marquette  dis- 
trict, but  it  is  similar  in  all  essential  respects  to  the  unconformity  between 
the  Lower  Huronian  cliertv  limestone  formation  in  the  Penokee  disti'ict 
and  the  overlying  quartz-slate  member  of  the  Upper  Huronian.  In  the 
Marquette  district  the  unconformity  is  indicated  by  a  marked  discordance 
between  the  upper  members  of  the  lower  series  and  the  lowest  members 
of  the  upper  series,  and  by  the  presence  of  a  widespread  basal  conglom- 
erate in  the  upper  seines.  In  the  Penokee  district  it  is  indicated  by  an 
erosion  contact  between  the  limestone  and  the  quartz-slate  without  dis- 
cordance of  bedding,  and  by  the  presence  of  fragments  of  the  lower  for- 
mation in  the  lowermost  beds  of  the  overlying  slates."  In  the  Menominee 
district  the  direct  evidence  of  the  unconformity  is  the  presence  of  a  con- 
glomerate or  of  a  coarse  quartzite  at  the  base  of  the  upper  series  containing 
undoubted  fragments  of  some  of  the  rocks  of  the  lower  series,  and  the 
jjresence  near  the  base  of  this  series  of  an  iron  formation  made  up  in  part  of 
the  detritus  of  an  older  iron  formation.  There  is  also,  in  addition,  indirect 
evidence  of  the  unconformity  in  the  absence  from  parts  of  the  district  of  the 
lowest  and  most  resistant  members  of  the  Algoiikian  series — the  Sturgeon 
quartzite  and  the  Randville  dolomite.  The  nonexistence  of  the  iron-bearing 
Vulcan  formation  in  parts  of  the  district  adjacent  to  the  Randville  dolomite 
and  the  overlapping  of  the  Vulcan  formation  by  the  Hanbur}-  slate  at  some 
of  these  places  give  further  evidence  of  unconformity.  The  Algonkian 
system  is  therefore  divided  into  a  Lower  Menominee  and  an  Upper  Menom- 
inee series,  equivalent  to  the  Lower  Huronian  and  tlie  Upper  Huronian 
elsewhere  in  the  Lake  Superior  region. 

The  data  upon  which  the  foregoing  conclusions  are  based  are  discussed 
in  detail  in  connection  with  the  descriptions  of  the  several  formations  com- 
prising the  different  systems  under  the  heading  "Relations  to  adjacent 
formations." 

SECTION  1.  liOWER  MENOMINEE  SERIES. 

Succession  and  distribution. — The  Lower  j\Ienominee  series  is  divided 
into  three  formations.  These  are,  in  the  order  of  upward  succession,  the 
Sturgeon  quartzite,  the  Randville  dolomite,  and  the  Negaunee  formation. 


o  Irving,  R.  D.,  and  Van  Hise,  C.  R.,  The  Penokee  iron-bearing  series  of  Michigan  and  Wis- 
consin: Hon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  pp.  171,  443-444,  454-455,  and  472. 


ALGONKIAN,  STURGEON  QUARTZITE.  177 

The  formatious  belonging  to  the  Lower  Menominee  are  observed  only 
in  the  center  and  on  the  northern  side  of  the  Menominee  trough.  On  the 
southern  side  of  the  trough  and  around  the  borders  of  the  western  area  of 
Quiunesec  schists  no  evidence  of  the  existence  of  these  formations  is  obtain- 
able. This  may  possibly  be  due  to  the  thick  covering  of  drift  that  blankets 
the  rocks  in  these  portions  of  the  district,  bnt  since  ledges  of  the  soft 
Hanbury  slate  are  found  at  no  great  distance  from  the  borders  of  the  schist 
areas,  it  is  probable  that  the  two  formations  are  actually  absent.  For  it  is 
hardly  credible  that  two  such  resistant  formations  as  the  quartzite  and 
dolomite  could  have  been  so  completely  planed  down  in  these  particular 
portions  of  the  area  as  to  leave  no  projecting  ledges  above  the  drift,  while 
soft  slate  formations  nearby  resisted  planation  sufficiently  successfully  to 
yield  ledges,  especially  since  in  the  central  and  northern  portions  of  the 
trough  the  quartzite  and  dolomite  constitute  the  prominent  elevations  and 
the  slates  the  valleys  between  these. 

STURGEON  QUARTZITE. 

The  Sturgeon  quartzite  is  so  called  because  the  principal  rock  of  the 
formation  is  a  quartzite  which  is  in  the  same  position  with  respect  to  the 
Archean  complex  and  the  dolomite  formation  of  the  Menominee  district  as 
is  the  Sturgeon  quartzite  of  the  Felch  Mountain  district  with  respect  to  the 
Archean  series  and  the  dolomite  of  that  district." 

DISTRIBUTION  AND  TOPOGRAPHY. 

The  Sturgeon  quartzite  forms  an  almost  continuous  belt  on  the  north 
side  of  the  Menominee  trough  immediately  south  of  the  northern  Archean 
complex,  with  which  it  is  in  contact.  Its  most  easterly  known  exposures 
are  in  the  center  of  sec.  9,  T.  38  N.,  R.  28  W.  From  this  point  the  belt 
continues  in  a  general  northwesterly  direction  to  sec.  2,  T.  40  N.,  R.  30  W., 
with  an  average  width  of  a  little  less  than  one-fourth  of  a  mile.  In  its 
eastern  portion  the  belt  is  narrow,  rarely  reaching  a  breadth  of  one-fifth  of 
a  mile.  As  it  joasses  west,  however,  it  gradually  widens  out,  and  in  sec.  2, 
T.  40  N.,  R.  SO  W.,  it  has  a  width  of  a  mile.  Here  the  belt  turns  north 
and  the  rock  is  folded  into  many  pitching  folds  which  cause  repetitions  of 
the  same  beds  and  a  great  increase  in  the  apparent  thickness  and  conse- 

"Mon.  U.  S.  Geol.  Survey,  vol.  36,  1899,  pp.  ,398-405. 
MON   XLVI — <A 12 


178  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

quently  iu  the  width  of  the  foi'ination.  For  2  miles  northward  exposures 
of  the  quartzite  are  very  abundant,  but  near  the  north  hne  of  sec.  29,  T.  41 
N.,  R.  29  W.,  it  disappears  under  a  covering  of  the  characteristic  micaceous 
quartzite  of  the  Calumet  trough,  believed  to  belong  iii  the  Upper  Menominee 
series. 

Throughout  the  distance  of  16  miles  between  the  eastern  end  of  the 
quartzite  belt  and  the  north  line  of  sec.  29,  T.  41  N.,  R.  29  W.,  where  it 
suddenly  ends,  the  belt  is  marked  by  an  almost  unbroken  succession  of  g-reat, 
bare,  rugged  bluffs  with  smooth  tops  and  almost  precipitous  sides,  especially 
to  the  south,  cut  here  and  there  by  deep,  narrow  gorges,  or  by  a  series  of 
small,  low  ledges  separated  from  one  another  by  stretches  of  glacial  sands. 
In  only  one  place  is  there  a  notable  gap  between  neighboring  exposures. 
The  belt  should  extend  through  sees.  34  and  35,  T.  40  N.,  R.  30  W.,  and  sec. 
2,  T.  39  N.,  R.  30  W.  Ledges  of  quartzite  are  found  iu  the  northeast  quarter 
of  sec.  2  and  in  the  northwest  quarter  of  sec.  34,  but  in  the  intervening  mile 
and  a  half  no  exposures  have  been  found.  To  the  north  are  the  usual  knolls 
of  the  Archean  gneisses  and  schists.  The  absence  of  exposure  may  be  due 
to  the  erosion  that  occurred  between  the  Lower  and  the  Upper  Menominee 
times  and  the  consequent  cutting  out  of  the  quartzite  at  this  place,  or  it 
may  be  that  the  formation  exists  deeply  buried  beneath  the  sands.  There 
is  a  marked  contrast  between  the  topograjjhy  of  this  portion  of  the  belt  and 
the  remaining  portions.  Instead  of  the  southward-facing  cliffs  that  are  so 
prominent  a  feature  of  the  area  underlain  by  the  quartzite  elsewhere  we  see 
here  a  stretch  of  sand  plain  whose  surface  is  100  feet  or  more  below  the 
level  of  the  surrounding  gneiss  and  quartzite  hills.  It  is  true  that  two  small 
streams  cross  the  area  at  right  angles  to  the  strike  of  the  belt,  and  these  may 
have  lowered  the  surface  to  its  present  position.  When  we  consider,  how- 
ever, that  the  Sturgeon  River,  where  it  crosses  the  quartzite,  has  produced 
no  such  effect,  and,  furthermore,  when  we  note  that  the  gneiss  and  granite 
still  exist  as  rugged  hills,  Avhose  elevation  is  practically  that  of  the  neigh- 
boring gneiss  and  granite  hills  at  some  distance  from  these  streams,  the 
conclusion  that  the  quartzite  did  not  exist  at  this  place  when  the  present 
topography  was  produced  seems  to  be  the  more  reasonable  of  the  two 
alternatives.  There  is  no  direct  evidence  as  to  the  presence  of  the  quartzite 
under  the  sand. 


ALGONKIAN,  STURGEON  QUARTZITE.  179 


LITHOLOGY. 


The  Sturgeon  quartzite  comprises  conglomerates,  quartzites,  quartz- 
schists,  arkoses,  graywackes,  and  dolomitic  sandstones  or  quartzites.  It  is 
cut  by  a  few  basic  dikes  and  by  veins  of  quartz. 


CONGLOMERATES. 


The  conglomerates  occur  only  in  a  few  places  very  near  the  granite- 
schist  complex.  They  are  well  exposed  on  the  flanks  of  this  complex  near 
the  north  quarter  post  of  sec.  32,  T.  41  N.,  R.  29  W.,  near  the  south 
quarter  post  of  sec.  6,  T.  39  N.,  R.  28  W.,  near  the  west  quarter  post  of  sec. 
1,  T.  39  N.,  R.  29  W.,  and  in  the  north  half  of  sec.  8,  T.  39  N.,  R.  28  W., 
in  which  is  the  famous  locality  at  the  Falls  of  the  Stm-geon.  In  all  these 
places  the  rock  is  composed  of  gneiss,  granite,  and  quai-tz  pebbles  and 
bowlders  in  a  groundmass  that  is  sometimes  an  arkose,  sometimes  a  gray- 
wacke,  and  occasionally  a  quartzite.  The  fragments  vary  in  size  from  a 
few  inches  to  a  foot  and  a  half  in  diameter.  Some  of  them  are  well 
rounded,  while  others  are  sharp  edged.  The  matrix  in  which  they  are 
embedded  is  sometimes  a  white  quartzite,  but  usually  it  is  dark  colored, 
being  either  dark  red  or  dark  gray,  according  to  the  predominance  in  it  of 
red  feldspar  grains  or  of  chloritic  or  micaceous  particles  derived  from  the 
decomposition  of  this  mineral.  The  darker-colored  matrices  are  also 
schistose,  the  schistosity  being  generally  parallel  to  their  contacts  with  the 
granite-gneiss  complex. 

The  character  of  the  conglomerates  varies  mainly  with  respect  to  the 
groundmass.  This  may  have  the  composition  of  a  quartzite,  an  arkose,  or 
a  graywacke,  and  it  may  either  be  massive  or  schistose.  The  conglomer- 
ates with  a  quartzitic  matrix  are  usually  massive  in  structure,  while  those 
with  an  arkose  or  graywacke  matrix  are  always  more  or  less  schistose. 
The  included  pebbles  are  in  all  instances  fragments  of  gneiss,  granite,  basic 
schists,  and  vein  quartz,  identical  with  the  corresponding  rocks  in  the 
Archean  complex. 

The  quartzitic  conglomerates  are  simply  quartzites,  like  the  normal 
rock  of  the  formation  described  below,  containing  pebbles  and  bowlders  of 
granite,  vein  quartz,  and  crystalline  schists,  together  with  irregular  g-rains 
of  the  individual  components  of  the  first-named  rock. 


180  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  greater  number  of  conglomerate  specimens  contain  a  large  quan- 
tity of  feldspar  in  their  groundmass.  Sometimes,  as  has  been  stated,  the 
matrix  has  the  composition  of  a  recomposed  granite  or  arkose,  and  at  other 
times  its  composition  is  more  nearly  that  of  a  graywacke."  Whether  the 
matrix  is  arkose-like  or  graywacke-like  appears  to  depend  upon  the 
character  of  the  Archean  shore  line  against  which  it  ^Yas  deposited.  Where 
the  Archean  rocks  in  contact  with  the  conglomerates  are  mainly  granites 
and  gneisses,  the  matrix  of  the  fragraental  rock  contains  large  quantities 
of  orthoclase — is  an  arkose.  On  the  other  hand,  where  the  Archean  rocks 
are  largely  greenstones,  the  matrix  contains  chlorite  and  the  decomposi- 
tion products  of  plagioclase — is  a  graywacke.  In  both  cases  the  stiiicture 
is  usually  schistose. 

The  larger  pebbles  in  these  conglomerates  jiossess  their  original  char- 
acter. The  smaller  ones,  however,  show  plainly  the  effects  of  mashing. 
The  quartz  pebbles  are  crushed  into  fragments,  which  are  sometimes  sepa- 
rated from  one  another  Ij}'  portions  of  the  groundmass,  but  which  are 
as  frequently  aggregated  into  groups  of  variously  oriented  grains,  differing 
in  outline  from  the  original  pebbles  in  being  much  elongated,  often  to  the 
extent  of  becoming  almost  vein-like.  The  particles  of  the  aggregates  are 
crossed  l)y  strain  shadows,  and  the  whole  appearance  of  the  quartz  suggests 
pressure  phenomena. 

The  smaller  granite  and  gneiss  pebbles  are  likewise  shattered.  Their 
individual  components  occur  as  sharp-edged  fragments  scattered  through 
the  matrix  at  intervals.  The  plagioclase  and  the  microcline  are  still  fresh, 
but  the  orthoclase  has  been  changed  to  a  micaceous  aggregate  of  secondary 
products,  in  which  particles  of  muscovite,  kaolin,  chlorite,  and  quartz  may 
be  detected. 

The  matrix  surrounding  the  pebbles  is  composed  of  isolated  grains  of 
quartz,  microcline,  and  plagioclase  in  an  extremely  fine-grained  groundmass 
that  hes  nearly  the  composition  of  an  altered  feldspar.  In  the  darker- 
colored  phases  of  the  rocks  there  is  in  addition  to  the  usual  decomposition 
products  of  feldspar,  quite  a  little  chlorite,  and  other  greenish  alteration 
products  of  biotite.    All  these  components  are  arranged  in  a  rudely  parallel 

"  The  term  graywacke  is  here  used  in  the  sense  in  which  it  has  been  defined  by  Geikie  and  J. 
Koth,  and  in  the  sense  in  which  it  has  been  used  in  the  description  of  the  Survey's  "Educational 
series  o£  rock  specimens,"  i.  e.,  as  a  fragramental  rock,  the  cement  of  which  is  dark  colored  and  of  the 
composition  of  a  clay-slate.     See  Bull.  U.  S.  Geol.  Survey  No.  150,  1898,  pp.  84-87. 


ALGONKIAN,  STURCtP:ON  QUARTZITE.  181 

direction,  which  is  approximately  parallel  to  the  direction  of  the  elongation 
of  the  crushed  quartz  fragments  derived  from  the  quartz  pebbles. 

The  coarser  grains  of  the  matrix  evidently  represent  sand  grains  in  a 
sediment  that  consisted  largely  of  the  material  from  which  the  finer  portion 
of  the  groundmass  was  produced.  This  must  have  been  a  mud  or  silt 
which  was  made  up  of  the  finer  detritus  of  the  Archean  rocks,  and  which 
was  therefore  comparatively  rich  in  ferronaagnesian  components. 

ARKOSES   AND    GRAYWACKES. 

The  conglomerates  pass  rapidly  into  nonconglomeratic  beds,  whose 
composition  is  like  that  of  the  conglomerate  groundmass.  In  some  places 
the  nonconglomeratic  rock  is  a  red  massive  or  schistose  arkose ;  in  other 
places  it  is  a  dark -gray  schistose  graywacke;  and  in  still  other  places,  it  is 
a  massive  or  schistose  light-gray  quartzite,  according  as  the  matrix  of  the 
conglomerate  associated  with  it  is  coarse  or  fine,  feldspathic  or  quartzitic, 
massive  or  schistose.  These  rocks  are  interbedded  with  the  conglomerates 
in  comparatively  thin  layers.  They  are  more  common  in  the  upper  portion 
of  the  conglomerate  beds  than  at  lower  horizons  and  constitute  gradation 
phases  between  the  conglomerates  and  the  tyjjical  quartzites. 

The  gradations  can  be  best  seen  at  the  Falls  of  the  Sturgeon  River, 
where  there  is  a  fairly  continuous  exposure  from  the  conglomerate  into  the 
quartzite,  through  transition  phases  that  are  rocks  like  the  matrix  of  the 
conglomerate.  The  rock  immediately  above  the  conglomerate  is  a  bright 
red  arkose;  above  this  is  a  fairly  massive  gray  graywacke  containing 
here  and  there  little  nests  of  pink  calcite;  and  above  this  again  a  schistose 
phase  of  the  same  rock.  The  next  layer  above  the  schistose  graywacke  is 
a  bright  red  arkose,  which  grades  through  a  light-gray  schistose  quartzite 
into  the  normal  vitreous  rock. 

There  are  very  few  of  the  arkoses  that  are  not  schistose.  Their 
feldspathic  constituent  furnished  abundant  material  for  the  production  of 
micaceous  products,  and  these,  under  the  influence  of  shearing  stresses, 
readily  took  on  the  parallel  arrangement  which  gave  rise  to  the  schistose 
structure.  In  their  present  condition  they  are  feldspathic  sericite-schists. 
The  few  massive  arkoses  met  with  appear  as  thin  beds  of  fairly  coarse- 
grained pink  rocks  lying  between  thicker  beds  of  qiiartzite.  The  more 
purely  quartzitic  phases  contained  but  little  feldspar;  consequently  there 
was  less  solution  of  their  constituents  and  therefore  a  smaller  production  of 


182  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

mica.  These  rocks  are  therefore  only  rarely  schistose,  except  along-  their 
shearing  zones  boiinding  joint  cracks  along  which  readjustment  took  place 
during  folding. 

In  thin  section  the  arkoses  are  seen  to  be  composed  of  quartz  grains 
and  fragments  of  orthoclase,  various  plagioclases,  microcline,  and  micro- 
perthite,  in  a  matrix  of  finer  grains  of  the  same  substances  colored  red  by 
iron  oxides.  Magnetite  crystals,  clumps  of  rutile,  an  occasional  crystal  of 
zircon,  and  a  few  grains  of  epidote  are  the  only  other  constituents  notice- 
able, except  certain  micaceous  decomposition  products  of  the  feldspars. 
These  are  especially  abundant  in  the  finest-grained  portions  of  the  matrix, 
which  in  many  places  is  composed  almost  exclusively  of  kaolin,  sericite, 
and  quartz.  Tlie  larger  feldspar  grains  are  often  quite  fresh,  the  plagio- 
clases and  the  microcline  being  almost  devoid  of  alteration  products  of  any 
kind.  The  orthoclase,  on  the  contrary,  is  usually  much  altered,  even  in 
the  largest  grains.  None  of  the  grains  are  as  completely  waterworn  as 
those  in  the  typical  quartzite.  They  are  usually  much  more  angular  than 
the  latter,  like  grains  of  sand  that  have  not  traveled  far  from  the  coast 
along  which  they  were  formed. 

The  graywackes  are  darker  than  the  arkoses.  They  are  always  schis- 
tose and  fine  grained.  The  schistosity  can  be  seen  to  arise  from  the 
parallel  arrangement  of  tin}^  shreds  and  plates  of  chlorite  and  some  light- 
colored  mica,  and  in  all  cases  where  it  has  been  carefully  examined  it  is 
parallel  to  the  bedding.  The  graywackes  are  always  finer  grained  than 
the  arkoses.  A  few  large  quartz  grains  are  scattered  through  them, 
but  the  main  portion  of  the  rocks  consists  of  small  grains  of  quartz  and 
decomposed  feldspars,  spicules  of  muscovite,  chlorite,  and  green  biotite, 
crystals  and  grains  of  magnetite,  little  nests  of  calcite,  and  occasionally 
a  small  prism  of  tourinaline. '  Much  of  the  quartz  of  the  groundmass  seems 
to  be  secondary,  as  it  is  in  the  form  of  interlocking-  areas  traversed  by  tlie 
micaceous  spicules. 

The  schistose  structure  is  produced  in  part  by  the  parallel  arrang-ement 
of  the  chloritic  and  micaceous  minerals  and  in  part  by  original  sedimenta- 
tion, for  there  is  often  noticeable  in  the  sections  alternating  layers  of  finer- 
and  coarser-grained  components  and  layers  containing  more  or  less  of  the 
quartz  and  feldspathic  constituents. 


ALGONKIAN,  STURGEON  QUARTZITE.  183 

QUAETZITE. 

The  major  portion  of  the  Sturgeon  formation  consists  of  massive  beds 
of  a  very  compact  quartzite.  As  a  rule  the  quartzite  is  entirely  massive, 
but  in  a  few  places  it  is  schistose.  Usually  the  schistose  phases  are 
feldspathic  and  sericitic,  and  they  are  nearly  always  associated  with  the 
conglomerates.  In  a  sense  they  appear  to  be  gradation  phases  between 
those  rocks  which  are  always  feldspathic  and  the  vitreous  massive 
quartzites.  Hence  they  are  found  only  in  the  lower  portion  of  the 
formation.  One  of  the  best  illustrations  of  the  schistose  quartzite  is  the 
ledge  sepai-ating  the  upper  from  the  lower  basin  below  the  Falls  of 
the  Sturgeon  River.  This  schist  is  a  very  fine-grained,  saccharoidal  dark- 
gray  rock  with  a  silky  luster  on  its  indistinct  cleavage  planes,  due  to  the 
presence  of  some  sericitic  mineral  in  plates  lying  parallel  to  the  cleavage. 
Above,  the  quartzites  pass  into  dolomitic  sandstones  by  the  gradual 
replacement  of  their  siliceous  cement  by  dolomitic  material. 

The  normal  rock  is  a  very  pure  quartzite,  composed  almost  exclusively 
of  quartz  grains  cemented  by  quartz.  Its  material  appears  to  have  been 
well  sorted,  practically  all  the  feldspar  grains  and  easily  decomposable 
substance  having  been  removed  from  the  sands  before  they  were  deposited 
in  their  present  position. 

The  rock  is  either  vitreous  or  saccharoidal.  It  is  usually  white  or 
Hght  gray  in  color,  but  many  beds  are  tinged  with  a  faint-pink  shade,  and 
occasionally  a  bed  is  observed  that  is  distinctly  green.  One  such  bed  is 
interleaved  with  ripjDle-marked  beds  of  snow-white  phases  of  the  rock  in 
the  small  knob  1,250  paces  north,  250  paces  west  of  the  southeast  corner 
of  sec.  2,  T.  39  N.,  R.  29  W. 

As  a  rule  the  quartzites  exhibit  little  evidence  of  mashing.  Their 
components  are  large  and  small  rounded  quartz  grains  cemented  together 
by  quartz  material  that  is  optically  continuous  with  the  grains  it  surrounds. 
Many  of  the  grains  are  beautifully  enlarged,  the  added  quartz  often 
building  them  out  into  well-proportioned  crystals.  In  the  pink  and  white 
varieties  of  the  rock  no  other  constituents  are  present  except  here  and 
there  a  grain  of  pyrite  or  a  small  spicule  of  chlorite. 

The  green  quartzite  referred  to  in  a  previous  paragraph  contains,  in 
addition  to  the  quartz,  a  considerable  quantity  of  light-green  sericite, 
forming  a  very  spai'se  interstitial  filling  between  the  quartz  grains      Under 


184  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

high  powers  of  the  microscope  this  mineral  appears  as  a  thick  felt  of 
spicules  traversing  the  cementing  quai'tz  and  penetrating  for  short  distances 
into  the  quartz  grains.  In  those  cases  where  two  grains  are  contiguous 
with  no  recognizable  intervening  cement,  the  line  of  junction  between 
them  is  marked  by  a  very  thin  film  of  needles  which,  to  all  appearances, 
have  been  formed  by  corrosion  of  the  quartz.  The  needles  penetrate  the 
quartz  on  both  sides  of  the  junction  line,  destroying  tlie  rounded  outlines 
of  the  grains  and  producing  very  ragged  ones.  The  phenomenon  looks 
very  much  as  though  produced  by  corrosive  jDrocesses — as  though  decom- 
position of  the  quartz  had  been  brought  about  through  solutions  passing 
between  the  grains  and  reacting  on  the  walls  of  the  tiny  canals  through 
which  the}'  flowed.  Single  flakes  of  the  sericite  are  occasionally  included 
within  the  grains,  and  little  clumps  of  rutile  are  found  in  the  midst  of  the 
felt  ill  the  large  interstices. 

In  the  schistose  quartzites  the  proportion  of  sericite  is  very  large,  and 
the  crushing  of  the  quartz  grains  is  very  noticeable.  The  rocks  consist 
essentially  of  sharp-edged  fragments  of  quartz  embedded  in  a  ground- 
mass  of  sericite  and  very  fine  quartz  grains.  The  larger  quartzes  are 
evidently  fragments  that  have  been  rubbed  together,  producing  by  their 
attrition  the  finer  grains  that  are  mingled  with  the  mica  in  the  groundmass. 
This  mica,  in  all  probability  muscoAdte,  is  in  exceedingly  large  quantities. 
It  occurs  as  tiny  colorless  spicules  and  fair-sized  plates,  forming  a  matted 
felt,  in  whose  meshes  are  tiny  grains  of  quartz.  The  mica  fibres  penetrate 
the  borders  of  the  larger  quartz  grains  like  those  in  the  green  quartzite 
described  above,  so  that  the  outlines  of  all  grains  are  exceedingly  ragged. 

A  very  noticeable  feature  in  the  schistose  quartzites  at  the  Falls  of  the 
Sturgeon  River  is  the  presence  of  large  pieces  of  a  brown-blue  tourmaline, 
idioinorphic  in  cross  section.  These  are  found  only  in  the  mica-quartz 
matrix.  They  are  much  larger  than  the  components  of  this  matrix  and 
were  evidently  formed  after  them.  They  possess  the  characteristic  sponge- 
like or  cellular  structure  of  contact  minerals,  and  are  distributed  indiscrimi- 
nately in  the  rock  without  respect  to  its  schistosity. 

The  schistosity,  which  is  so  noticeable  in  some  hand  specimens  of  these 
rocks,  is  not  a  marked  feature  of  the  thin  sections.  It  is  produced  by  the 
arrangement  of  a  small  majority  of  the  mica  flakes  in  parallel  positions 
and  the  elongation  of  a  few  of  the  quartz  grains  in  the  same  direction. 


ALGONKIAN,  STURGEON  QUARTZITE.  185 

DOLOMITIC   QUARTZITE. 

The  dolomitic  quartzites  are  intermediate  in  character,  as  they  are 
intermediate  in  position,  between  the  normal  quartzites  below  them  and  the 
dolomite  of  the  Randville  formation  above  them. 

In  its  upper  portions  the  cement  between  the  quartz  grains  of  the 
quartzites  is  often  dolomitic.  This  carbonate  constituent  increases  in 
quantity  as  the  overlying  dolomite  is  approached,  until  the  rock  becomes  a 
dolomitic  quartzite  and  finally  a  quartzose  dolomite.  In  the  hand  specimen 
the  carbonate  phases  may  usually  be  easily  distinguished  from  the  normal 
quartzites  by  their  porosity.  Where  the  rock  has  not  been  exposed  to  the 
weather  for  any  great  time  it  is  quite  compact,  but  on  its  exposed  surface 
maj  be  detected  numerous  little  pits  that  have  resulted  from  the  solution 
of  the  carbonate  cement  from  between  the  quartz  grains.  When  the 
weathering  has  been  more  profound  the  rock  has  lost  its  compactness  and 
is  now  a  friable  mass  of  loosely  cohering  sand  grains. 

In  thin  sections  the  dolomitic  quartzites  consist  of  quartz  grains  lying 
in  a  dolomitic  cement.  They  present  no  specially  noticeable  features. 
The  presence  of  these  rocks  at  the  top  of  the  Sturgeon  formation  points 
to  a  gradual  deepening  of  the  waters  in  preparation  fur  the  succeeding 
deposition  of  the  Randville  dolomite. 

VEINS   AND    DIKES   IN   THE    QUARTZITE. 

In  general  the  Sturgeon  quartzite  is  devoid  of  intersecting  rock  masses. 
However,  in  the  close  folds  already  referred  to  as  existing  in  the  northeast 
portion  of  T.  40  N.,  R.  30  W.,  and  southwest  portion  of  T.  41  N.,  R.  29  W., 
the  quartzite  is  much  fissured  by  quartz  veins  of  various  widths,  which 
in  some  places  are  so  numerous  and  close  together  as  to  form  a  breccia 
of  quartzite  fragments  in  a  quartz  cement.  Some  of  these  quartz  veins 
contain  small  quantities  of  free  gold,  as  does  also  the  quartzite  in  their 
vicinity.  An  attempt  was  made  a  few  years  ago  to  work  them,  but  the 
venture  was  not  profitable  and  was  therefore  abandoned. 

In  this  portion  of  the  quartzite  area  intrusions  of  a  dark-colored  dia- 
base are  also  ver}'  prominent.  They  occur  as  narrow  dikes  traversing  the 
quartzite  and  the  underlying  gneiss,  and  also  as  boss-like  masses  partially 
surrounded  b}'  the  quartzite,  or  as  small  isolated  knobs  separated  from  one 


186  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

another  and  from  neighboring  quartzite  ledges  by  stretches  of  surface  free 
from  exposures. 

At  one  other  place,  near  the  south  quarter  post  of  sec.  6,  T.  39  N.,  R. 
28  W.,  the  conglomerates  and  quartzites  are  cut  by  a  very  large  dike  of 
coarse-grained,  black  gabbro  that  extends  across  the  contact  between  the 
two  rocks  nearly  at  right  angles  to  the  strike  of  the  quartzite  and  traverses 
nearly  the  entire  breadth  of  this  formation. 

At  no  other  places  were  intrusives  noted  in  the  quartzite. 

FOLDING. 

Except  for  a  slight  divergence  of  strike  in  the  quartzite  beds  outcrop- 
ping in  sec.  7,  T.  39  N.,  R.  28  W.,  there  is  no  certain  indication  of  folding 
in  the  entire  quartzite  belt  from  its  eastern  end  in  sec.  9,  T.  39  N.,  R.  28  W., 
to  the  point  in  the  southeast  quarter  of  sec.  2,  T  40  N.,  R.  30  W.,  where  it 
turns  north  into  the  Calumet  trough.  In  all  this  distance  the  beds  are 
practically  monochnal,  with  dips  varying  between  65°  and  90°.  Moreover, 
there  are  nearly  as  many  dips  northward  toward  the  granite-gneiss  complex 
as  there  are  southern  dips  away  from  it.  In  the  northeast  quarter  of  sec. 
7,  T.  39  N.,  R.  28  W.,  however,  there  is  a  large,  bare  knob  of  quartzite 
showing  a  slight  divergence  in  the  beds,  which  indicates  that  cross  folding 
has  taken  place  to  some  extent.  The  general  strike  of  the  bedding  is  N. 
65°  "W.  (25°  N.  of  W.),  but  in  the  southeast  portion  of  the  knob  the  strike 
is  N.  75°  E.  (15°  S.  of  W.),  a  variation  of  40°  from  the  general  strike. 
Furthermore,  the  general  dip  of  the  rock  is  75°  to  90°  N.,  while  the  dip  of 
the  beds  striking  S.  of  W.  is  70°  S.  These  observations  are  not  sufficient 
to  establish  the  nature  of  the  fold  at  this  place,  but  they  are  significant  in 
that  they  point  to  the  possible  existence  of  close  folds  in  the  series. 

So  far  as  can  be  inferred  from  the  distribution  of  the  quartzite,  the 
formation  constitutes  the  north  limb  of  a  synclinal  fold  pitching  westward. 
Its  southern  limb  would  normally  appear  adjacent  to  the  Quinnesec  schists 
along  the  Menominee  River,  but  this  was  apparently  removed  by  erosion 
in  the  interval  between  Lower  Menominee  and  Upper  Menominee  times. 

At  the  western  end  of  the  district,  in  the  southeast  quarter  of  sec.  2, 
T.  40  N.,  R.  30  W.,  the  quartzite  turns  northward,  wrapping  around  the 
Archean  complex  and  then  passing  eastward  into  the  area"  of  the  Calumet 
trough  (see  PI.   XIV).     In  the    3   miles  occupied    in   the  turn  from  the 


U.   S.   GEOLOGICAL    SURVEV 


MONOGRAPH    XLVl       PL.   XIV 


\  /    Basic  iutrusi 


sic  iutrusives 


^  -^1  DolDinite 

Massive  quartzite 
Bedded  quartzite 
Conglomerate 
Granito-giieiss-schist 


SKETCH    MAP    OF    EXPOSURES    NEAR   THE   CONTACT    BETWEEN    THE   STURGEON    QUARTZITE   AND    THE 
ARCHEAN    COMPLEX,    IN   T.  40   N..    R.  30  W.,   AND  T.  41    N.,    R.  29  W. 


ALGONKIAN,  STURGEON  QUARTZITE.  187 

Menominee  trough  into  the  Cakimet  trough  the  margin  of  the  quartzite  is 
made  up  of  three  sahents  and  four  reentrants.  The  salients  extend  east- 
ward into  a  corresponding  number  of  embayments  in  the  gneiss-schist 
complex.  The  quartzite  is  evidently  closely  folded,  the  salients  consisting 
of  synclines  and  the  reentrants  of  anticlines,  but  the  rock  is  so  massive 
that  dips  and  strikes  are  not  easily  recognized.  It  is  plain,  however,  from 
a  consideration  of  those  observed,  that  the  synclines  pitch  steeply  to  the 
west,  for  the  points  from  which  the  platted  strikes  diverge — i.  e.,  the  apexes 
of  the  folds — are  at  some  distance  east  of  the  western  limits  of  the  Archean 
rocks  and  necessarily  above  their  present  surfaces. 

THICKNESS. 

In  the  attempt  to  calculate  the  thickness  of  the  quartzite  we  are  met  by 
two  difficulties.  The  first  is  the  impossibility  of  deciding  how  much  of  its 
apparent  thickness  is  due  to  tlie  duplication  of  beds.  At  one  jalace  we  have 
seen  that  duplication  is  probable.  Whether  there  is  a  repetition  of  the 
same  beds  in  other  portions  of  the  belt  or  not  we  can  not  be  certain.  A 
second  difficulty  arises  from  the  fact  that  we  are  imable  to  fix  definitely  the 
upper  limit  of  the  formation. 

If  we  assume  that  the  southward-facing  cliffs  which  so  frequently  mark 
the  southern  limit  of  the  quartzites  are  cliffs  of  differential  degradation,  tliat 
the  low  ground  at  the  base  of  the  cliff's  is  underlain  by  the  dolomite 
formation,  and  that  the  exposures  are  monoclinal,  the  thickness  of  the 
quartzite  may  be  easily  calculated  at  a  number  of  places.  At  the  gorge 
below  the  Falls  of  the  Sturgeon  River  in  the  northeast  quarter  of  sec.  8, 
T.  39  N.,  R.  28  W.,  is  a  continuous  exposure  of  conglomerate  and  quartzite 
beds  about  360  paces  in  width.  For  300  paces  the  walls  of  the  gorge  are 
in  even-bedded  quartzite,  striking  N.  57°  W.  and  dipping  75°  to  83°  N. 
An  inspection  of  these  beds  reveals  no  indication  of  folding.  The  formation 
in  its  entire  width  appears  to  consist  of  consecutive  beds.  The  thickness 
corresponding  to  this  width,  calculated  at  an  average  dip  of  80°,  is  915 
feet.  Approximately  tlie  same  result  is  reached  from  measurements  made 
on  the  east  side  of  the  river  a  few  hundred  feet  from  the  river  bank.  Here 
the  breadth  of  the  formation  is  400  paces  and  its  dip  70°  N.  The 
corresponding  thickness  is  about  1,050  feet. 

A  third  estimate  is  based  on   a  series  of  fine  exposures  in  the  south 


188  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

half  of  sec.  1,  T.  39  N.,  R.  29  W.  At  this  place  the  quartzite  has  a  very 
regular  bedding,  striking  N.  65°  W.  and  dipping  87°  S.  The  beds  are 
beautifully  ripple  marked  and  this  ripple  marking  is  so  perfectly  preserved 
that  it  is  very  difficult  to  believe  that  the  beds  have  ever  been  subjected  to 
such  close  folding  as  would  be  necessary  to  produce  in  them  a  uniform  dip 
throuffhout  their  entire  breadth.  The  width  of  the  belt  measured  across  the 
strike  of  the  quartzite  from  the  edge  of  the  granite-gneiss,  about  150  paces 
north  of  the  most  northerly  ledge  of  quartzite,  to  the  cliff  bordering  the 
quartzite  on  the  south,  is  about  500  paces.  The  equivalent  thickness  would 
be  about  1,250  feet. 

These  are  the  only  places  at  which  the  conditions  are  favorable  for  the 
measurement  of  the  thickness  of  the  formation.  It  is  probable  that  its 
thickness,  like  that  of  sedimentary  formations  elsewhere,  varies  in  different 
places,  but  it  seems  safe  to  presume  that  the  above  figures  represent  a  fair 
average  and  that  its  maximum  thickness  is  between  1,000  and  1,250  feet. 

RELATIOXS  TO  UNDERLYING  FORMATIONS. 

The  fact  that  conglomerates  occur  at  and  near  the  base  of  the  Stur- 
geon quartzite  has  already  been  mentioned,  and  the  locations  at  which 
some  of  them  occur  have  also  been  referred  to.  These  basal  conglomerates 
contain  almost  every  variety  of  fragment  derivable  from  the  rocks  of  the 
Northern  Complex.  Moreover,  the  material  of  the  fragments  exhibits  the 
same  secondary  structures  as  are  noticed  in  the  Archean  rocks.  Plainly, 
then,  the  Archean  had  reached  its  present  condition  before  the  conglomer- 
ates were  laid  down.  Furthermore,  some  of  the  Archean  rocks  must  have 
been  formed  at  great  depths  in  the  earth.  Therefore  the  Archean  area 
must  have  suffered  deep-seated  denudation  before  the  deposition  of  the 
quartzite.  The  presence  of  the  conglomerates,  then,  is  e^^dence  of  the 
existence  of  a  great  time  interval  between  the  production  of  the  granite- 
schists  complex  and  the  overlying  Sturgeon  quartzite.  A  consideration 
of  the  character  of  the  matrix  of  the  conglomerates  points  to  the  same  con- 
clusions. The  matrix  consists  largely  of  the  dcibris  of  granites,  gneisses, 
and  basic  schists;  or,  in  other  words,  of  sand  and  silt  such  as  would  be 
jDroduced  by  denudation  of  the  Archean  complex. 

Contacts  of  the  Sturgeon  quartzite  with  the  underlying  rocks  are  very 
rare.     They  are  found  only  where   the   conglomerates   are   present.     In 


ALGONKIAN,  STURGEON  QUARTZITE.  189 

these  cases  the  schistosity  of  the  conglomerates  is  discordant  with  that  of  the 
subjacent  gneisses  and  schists.  At  most  places  there  is  a  topographic 
depression  between  the  two  formations,  due,  no  doubt,  to  the  relative  ease 
with  which  the  conglomerates,  arkoses,  and  graywackes  are  eroded  as 
compared  with  the  adjacent  granites  and  schists  on  the  one  side  of  them 
and  the  pure  quartzites  on  the  other.  The  quartzites  on  the  south  of  the 
break,  however,  sometimes  strike  directly  toward  the  boundary  of  the 
granite-gneiss  complex.  This  may  indicate  an  unconformity  between  the 
two  series. 

INTERESTING  LOCALITIES. 

Although  the  quartzite  formation  is  well  exposed  throughout  nearly  its 
entire  extent,  there  are  several  localities  where  the  ex2Dosures  are  of  special 
interest,  either  because  of  the  relations  shown  in  them  or  because  of  the 
fine  expanse  of  rock  surface  they  exhibit. 

The  '■Wock  dam"  on  Pine  Creek. — One  of  the  best  places  at  which  to  study 
the  quartzitic  phase  of  the  formation  is  in  sec.  2,  T.  40  N.,  R.  30  W.,  and 
sees.  31  and  32,  T.  41  N.,  R.  29  W.  (PI.  XIV).  Here  is  found  the  greatest 
expanse  of  quartzite  occurring  anywhere  in  the  Menominee  district,  and 
the  wildest  and  most  pictm-esque  scenery.  Precipices,  crags,  and  gorges 
abound  everywhere.  The  precipices  are  so  steep  and  the  gorges  so  nan-ow 
that  the  snow-white  bluffs  appear  much  loftier  than  they  actually  are. 
Moreover,  the  effect  of  the  roughness  of  the  country  on  the  observer  is 
much  heightened  because  of  the  great  contrast  between  it  and  the  flat  sand 
plains  and  rounded  sand  hills  over  which  he  must  travel  to  reach  the 
quartzite  area. 

The  quartzite  forms  a  few  high,  bare  bluffs,  with  precipitous  sides  and 
broad,  flat  tops,  and  numerous  lower  and  smaller  hills,  often  with  uneven 
tops.  From  their  eastern  limits  bare  bluffs  of  black,  pink,  and  gray  Archean 
rocks  extend  eastward  for  long  distances.  To  the  west  the  bluffs  end 
abruptly,  and  a  comparatively  level  sand  plain,  dotted  with  low,  rounded 
sand  hills,  stretches  from  their  bases  and  gradually  I'ises  into  a  series  of 
smoothly  rounded  elevations  in  the  distant  west. 

The  boundary  line  between  the  quartzite  and  the  Archean  rocks,  unlike 
this  boundary  elsewhere,  consists  of  curves  with  broad  crests  turned  east- 
ward toward  the  Archean  complex,  and  sharp  crests  turned  westward  toward 
the  quartzite.  The  former  have  already  been  explained  as  due  to  synclines 
and  the  latter  to  anticlines  in  the  quartzites. 


190  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

The  principal  rock  of  the  bluffs,  as  has  been  intimated,  is  a  white 
saccharoidal  or  vitreous  quartzite.  This  is  so  heavily  bedded  that  only 
occasionally  can  strikes  and  dips  be  observed  in  it.  Where  they  can  be 
measured  they  are  found  to  vary  in  such  a  way  as  to  pi-ove  the  existence 
of  folds  with  westward-pitching  axes.  The  dips  vary  between  50°  and 
90°,  and  are  always  directed  to  the  south  or  west,  or  to  some  point  of  the 
compass  between  west  and  south.  The  strikes  vary  greatly.  Near  the 
southeast  corner  of  sec.  2,  T.  40  N.,  R.  30  W.,  the  strike  of  a  definitely 
bedded  quartzite  is  N.  50°  W.  Near  the  east  quarter  post,  sec.  31,  T.  41  N., 
R.  29  W.,  it  is  N.  45°  W.  Near  the  south  quai'ter  post  of  the  same  section 
it  is  N.  10°  E.,  and  about  one-fourth  mile  south  of  the  north  quarter  post, 
sec.  32,  T.  41  N.,  R.  29  W.,  it  is  N.  15°  W.  However  irregular  these  dips 
and  strikes  may  seem  at  first  tliought,  they  are  nevertheless  distributed  in 
accordance  with  the  view  suggested  as  to  the  structure  of  the  formation  at 
this  place. 

One  of  the  most  striking  of  the  quartzite  blufi"s  is  that  in  sec.  2,  T.  40 
N.,  R.  30  W.  It  is  a  bare,  rough  knoll  whose  southern  face  is  an  almost 
vertical  cliff'  rising  about  40  feet  above  the  bed  of  a  small  stream  that 
separates  the  quartzite  from  the  adjacent  gneisses  and  schists.  Farther 
west  the  cliff  is  less  nearly  vertical,  but  it  rises  to  greater  heights.  As  at 
this  place,  so  nearly  everj-where  else  in  this  portion  of  the  district,  the 
quartzite  and  the  granite-gneiss  complex  are  separated  from  one  another 
by  topographic  breaks  in  the  shape  of  narrow  valleys.  These  are  often 
but  20  to  100  paces  wide,  have  precipitous  sides,  and  are  usually  occupied 
by  the  channel  of  Pine  Creek  or  some  one  of  its  tributaries.  At  several 
places  the  streams  turn  abruptly  from  the  contact  valleys  and  cross  the 
quartzite  bluffs,  producing  in  them  likewise  narrow  gorges.  The  best 
example  of  one  of  these  cross  gorges  is  about  300  paces  north  of  the 
south  quarter  post,  sec.  31,  T.  41  N.,  R.  29  W.,  where  the  main  stream  of 
Pine  Creek  runs  for  a  short  distance  across  the  strike  of  tlie  quartzite 
between  walls  that  rise  nearly  100  feet  precipitously  from  the  stream's 
banks.  This  place  is  known  locally  as  the  "rock  dam."  The  rock  on  the 
weathered  surface  of  the  bluffs  through  which  the  gorge  is  cut  is  brilliantly 
grayish  white  and  very  massive,  only  here  and  there  exhibiting  any  signs 
of  bedding.  When  the  bedding  is  noticeable  the  beds  are  seen  to  be 
nearly  on  end.     Two  dominant  sets  of  joints  traverse  them,  both  of  whicli 


ALGONKIAN,  STURGEON  QUARTZITE.  191 

are  vertical.  One  set  runs  parallel  to  the  creek,  i.  e.,  about  east  and  west, 
and  the  other  is  at  right  angles  to  this,  in  places  apparently  following  the 
bedding.  It  is  the  opening  up  of  one  of  the  former  l)y  the  stream  that 
produced  the  gorge  at  the  rock  dam.  Besides  these  two  vertical  systems 
of  joints  there  is  a  marked  sheeting  or  schistose  structure  to  the  quartzite 
which  dips  to  the  west  at  low  angles  (8°  to  10°).  The  structure  produces 
layers  from  1  to  2  feet  across,  separated  from  one  another  at  intervals 
by  joints.  They  are  so  distinct  that  they  might  easily  be  mistaken  for 
beds.  This  apparent  bedding  is  no  doubt  due  to  differential  movement 
parallel  to  the  axis  of  a  large  fold.  The  rock  at  this  place  is  near  the  top 
of  an  anticline  plunging  to  the  west.  Accommodation  must  have  taken 
place  parallel  to  this  direction  with  resulting  schistosity  along  the  zones  of 
rock  movement.  This  structure  must  have  been  produced  at  a  tinie  when 
the  rock  was  heavily  loaded.     The  joints  may  have  been  formed  later. 

The  quartzite  is  cut  by  many  white  quartz  veins  of  all  sizes  up  to  20 
feet  in  width.  Some  of  them  follow  the  jointing  systems  in  direction,  while 
others  cut  the  rock  irregularly.     In  some  of  these  gold  has  been  discovered. 

Although  the  quartzite  phase  of  the  formation  is  so  well  developed  in 
this  vicinity,  its  feldspathic  phases,  characteristic  of  the  lower  horizons,  are 
notably  absent  except  at  one  place.  They  were  no  doubt  originally  present 
in  the  interval  now  occupied  by  the  little  valleys  between  the  quartzite  and 
the  Archean  schists.  The  only  remnants  of  these  beds  still  remaining  are 
to  be  found  near  the  north  quarter  post  of  sec.  32,  T.  41  N.,  R.  29  W.  Here 
a  well-defined  conglomei-ate  composed  of  rounded  fragments  of  granite  and 
gneiss,  with  diameters  ranging  from  the  fraction  of  an  inch  to  1 J  feet,  lying- 
in  a  dark-gray  schistose  matrix,  occurs  in  patches  adhering  to  the  almost 
vertical  face  of  a  cliff  of  Archean  gneiss.  The  strike  of  the  schistosity  and 
banding  of  the  gneiss  is  N.  15°  E.  That  of  the  corresponding  structures  in 
the  conglomerate  is  parallel  to  the  trend  of  the  cliff,  which  varies  from  due 
north-south  to  nearly  east-west.  (See  PI  XIV  and  fig.  13.)  "While  the 
variation  in  the  strike  of  the  schistosity  of  the  two  rocks  may  not  in  itself 
necessarily  prove  the  existence  of  an  unconformity  between  them,  the 
presence  of  large  bowlders  of  the  gneisses  in  the  conglomerate  is  undoubted 
evidence  that  the  former  rocks  had  been  subjected  to  wave  action  before 
the  conglomerate  was  formed. 

The  conglomerate  and  the  gneiss  are  cut  by  a  dike  of  dark,  almost 


192 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


black,  diabase  trending  about  northwest.  Across  a  little  valley  the  same 
dike  can  be  traced  into  a  ledge  of  quartzite,  where  the  contrast  in  color 
between  the  two  rocks  is  very  strikingly  brought  out.  Again,  farther  south, 
there  is  a  large  dike  of  the  same  rock  trending  nearly  north-south.  This 
dike  is  just  west  of  the  one  of  the  larger  exposures  of  conglomerate,  which 


Fig.  13.— Sketch  map  of  exposure  in  north  half  of  sec.  32,  T.  41  N.,  E.  29  \V.,  showing  relation  between  conglomerates 

and  gneisses.    Scale:  1  inch  =  660  feet. 

thus  lies  between  the  igneous  rock  on  the  one  side  and  the  gneiss  on  the 
other,  a  position  which  has  protected  it  from  rapid  erosion. 

Farther  south,  especially  in  sec.  2,  T.  40  N.,  R  30  W.,  several  other 
masses  of  the  diabase  occur.  These,  however,  do  not  possess  the  dike  form 
of  the  more  northerly  masses.     They  appear  as  small,  isolated  knolls  rising 


ALGONKIAN,  STURGEON  QUARTZITE.  193 

above  the  sands,  except  in  one  instance,  where  the  rock  forms  a  huge  black 
boss-like  mass  in  contact  on  the  east  with  beds  of  snow-white  quartzite. 
The  parti-colored  knob  formed  of  the  two  rocks  can  easily  be  seen  from  the 
road  leading  to  the  "rock  dam."  It  is  a  prominent  object  in  the  landscape 
viewed  from  the  south  and  southwest,  even  at  distances  of  several  miles. 

Before  leaving  this  portion  of  the  district  it  might  be  well  also  to  refer 
to  one  other  exposure  which  may  be  considered  as  representing  the  upper 
members  of  the  Sturgeon  formation,  though  more  properly  belonging 
among  the  outcrops  of  the  next  higher  formation,  the  Randville  dolomite. 
The  ledges  are  near  the  northeast  corner  of  sec.  3,  T.  40  N.,  R.  30  W.,  and 
near  the  southwest  corner  of  sec.  31,  T.  41  N.,  R.  29  W.,  about  300  paces 
west  of  the  nearest  exposure  of  the  normal  quartzite.  They  constitute  a 
Htde  cliflf  overhanging  the  flood  plain  of  Pine  Creek.  The  top  of  the 
elevation  of  which  the  clitf  forms  the  eastern  escarpment  is  covered  with 
sand,  and  both  ends  of  the  cliff  tace  also  disappear  under  deposits  of  sand 
and  bowlders.  On  the  face  of  the  cliff,  however,  the  rocks  are  well 
exposed  for  a  distance  of  about  200  paces.  They  are  noticeably  different 
from  the  normal  quartzite,  even  when  viewed  from  the  road.  They 
weather  with  a  rough  sandy  surface  and  rounded  edges,  whereas  the 
quartzite  weathers  with  smooth  surfaces  and  sharp  edges.  Moreover, 
they  are  distinctly  bedded  and  plainly  folded.  When  examined  closely 
the  cliff  is  seen  to  be  made  up  of  a  calcareous  quartzite  containing  a  few 
thin  chei'ty  layers  and  in  the  upper  horizons  a  few  layers  of  red  slate.  The 
lowermost  exposed  layers  are  comparatively  flat  lying,  but  the  upper  layers 
are  in  a  series  of  westward-pitching  folds,  some  of  which  are  completely 
recumbent.  The  strikes  and  dips  are  therefore  very  different  in  different 
parts  of  the  ledge.  Opposite  the  bridge  over  Pine  Creek,  for  instance,  the 
strike  is  N.  55°  E.  and  the  dip  45°  northwest.  About  50  paces  south  of 
this  point  the  strike  is  N.  20°  E.  and  the  dip  20°  west,  and  about  100  paces 
farther  south  the  strike  is  N.  40°  W.,  and  the  dip  45°  southeast.  The 
weathered  surface  is  ridgy  with  alternate  elevations  and  depressions  about 
one-half  inch  to  1  inch  in  width,  produced  by  differential  weathering  of 
alternate  layers  that  are  usually  inclined  to  the  bedding.  Along  these 
layers  differential  movement  has  taken  place,  the  alternate  laminse  tlms 
becoming  more  or  less  schistose.  The  more  schistose  layers  representing 
zones  of  weakness   were  weatiiered   more    rapidly  than    the    others   and 

MON  XI, VI — 04 13 


194 


THE  MENOMINEE  IRON-BEAKING  DISTRICT. 


determined  the  position  of  the  depressions  in  the  surface.  Tliese  laminae, 
like  the  bedding  layers,  are  likewise  folded  into  minor  plications,  some  of 
which  are  clearly  recumbent  folds. 

Black  Creek. — About  260  paces  north  of  the  south  quarter  post  of 
sec.  6,  T.  39  N.,  R.  28  W.,  a  small  stream  known  localh^  as  Black  Creek, 
falls  in  a  little  cascade  over  a  ledge  composed  partly  of  granitoid  gneiss 
and  partly  of  conglomerate  (see  map,  fig.  14).  The  gneiss  is  of  the  usual 
character.  The  conglomerate  is  made  up  of  round  and  angular  fragments 
of  the  gneiss  strewn  thickly  through  a  matrix  composed  of  the  fine  detritus 
of  the  same  rock.  So  nearly  alike  are  they  in  general  appearance  that  at  a 
casual  glance  it  is  difficult  to  distinguish  between  the  original  rock  and  the 
recomposed  phase. 


0 

^e 

Scale                                 .,     1 
Vfi  milesi 

«-.*.                  i 

Wi    Gneiss 

'•■».. .m.A.m,  '„ \ 

^    Quartzite 

V^*"^* 

fl^  Conglomerate 

H"  Intrusive  gabbro 

/           ,<^  '■ 

Fig.  14. — Sketcli  map  of  exposures  on  Black  Creeli,  in  S.  i  sec.  6,  T.  39  N  .  R.  2.S  W..  .sliowing  relation  of  conglomerate 

to  gneisses. 

Associated  with  the  conglomerate  are  a  few  beds  of  a  banded  rock 
that  strike  N.  55°  W.  and  dip  nearly  vertical.  This  is  plainly  fragmental 
and  is  like  the  groundmass  of  the  conglomerate.  A  few  hundred  paces 
west  is  a  small  ledge  of  white  vitreous  quartzite  and  about  the  same  distance 
southwest  is  another  of  the  same  rock.  Neither  show  any  special 
peculiarity. 

The  contact  between  the  gneiss  and  the  conglomerate  is  not  well 
enough  exposed  to  give  an}-  xevy  clear  idea  of  the  structural  relations 
existing  between,  but  of  course  there  can  be  no  doubt  that  the  latter  is 
much  younger  than  the  former. 

Cutting  through  gneiss,  conglomerate,  and  quartzite  is  a  great  dike  of 
medium-  to  coarse-grained  black  gabbro.  In  the  gneiss  it  appears  as  an 
ordinary  dike  whose  upper  surface  is  flush  with  the  surface  of  the  surrounding 
rock.     As  it  crosses  the  conglomerate  it  forms  a  prominent  knob.     From 


ALGONKIAN,  STURGEON  QUARTZITE. 


195 


this  i^oint  it  continues  southwestward  as  a  ridge  of  knobs,  with  occasional 
quartzite  exposures  on  their  flanks. 

It  is  to  be  noted  here,  as  at  the  rock  dam,  that  the  conglomerate  which 
remains  is  in  a  position  where  it  was  protected  by  a  mass  of  igneous  rock. 

North  half  of  sec.  7,  T.  39  N.,  B.  28  W. — Southeast  of  the  exposures 
described  in  the  foregoing  paragraph  the  quartzite  forms  a  belt  of  cliffs  and 
bluffs  that  extends  for  over  a  mile  and  a  half  through  sees.  6  and  7  without 
interruption  except  at  one  place  where  it  is  trenched  b}^  the  Sturgeon 
River  (fig.  15).  Near  the  north  quarter  post  of  sec.  7  the  quartzite  is 
intruded  by  the   gi-eat  dike  of  gabbro  already  referred  to  in  connection 


Gneiss 
Quartzite 
Conglomerate 
Intrusive  diabase 


Pig.  15.— Sketch  map  of  exposures  at  and  near  the  Falls  of  the  Sturgeon  Klver,  sec.  8,  T.  39  N.,  R.  28  W. 

with  the  conglomerate  of  Black  Creek.  East  of  this  the  quartzite  constitutes 
a  long,  narrow  hill  with  a  very  steep  south  side  overhanging  the  swampy 
flood  plain  of  the  Sturgeon.  On  the  north  the  declivity  is  less  steep  but 
very  rugged.  The  rock  is  the  typical  white  vitreous  quartzite.  It  is 
nowhere  in  contact  with  the  granite,  a  space  of  about  200  paces  devoid  of 
exposures  usually  separating  the  two  rocks.  The  bluff  is  interesting  from 
the  fact  that  it  exhibits  strikes  and  dips  so  distributed  as  to  suggest  close 
folding  in  the  beds  of  which  it  is  composed.  Northwest  of  the  main  bluff 
are  several  ledges  near  the  gabbro,  in  which  the  bedding  strikes  N.  55°  "W. 
and  dips  87°  north      The  main  bluff  is  roughly  triangular  in  outline,  the 


196  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

western  end  being  about  300  paces  wide  and  the  eastern  end,  where  the 
east  line  of  the  section  crosses  it,  measuring  only  about  100  paces  in  width. 
On  the  south  side  of  the  hill,  in  its  eastern  part,  the  rock  in  the  cliff 
overlooking  the  river  strikes  N.  75°  E.  and  dips  75°  south,  whereas  the 
beds  on  the  north  side  strike  N.  60°  W.  and  dip  about  vertically.  Thus 
at  the  eastern  or  narrow  portion  of  the  bhiff  the  variation  in  strike  between 
the  beds  on  its  north  and  south  sides  is  about  45°.  Toward  the  west  the 
strike  of  the  southern  beds  turns  gradually  to  the  north,  and  at  the  west 
end  of  the  hill  its  entire  width  is  made  up  of  a  series  of  parallel  beds 
striking  uniformly  about  N.  35°  W. 

West  half  of  sec.  S,  T.  39  N.,  B.  28  W.—lw  a  hill  east  of  the  one  just 
described  quartzite  is  again  beautifully  exposed  in  well-bedded,  though 
massive,  layers  striking  about  N.  60°  W.  and  dipping  50°  to  75°  north. 
(See  map,  fig.  15.)  This  hill,  like  the  northwesterly  one,  is  precipitous  on 
both  north  and  south  sides.  To  the  north  of  it  is  the  granite-gneiss 
complex  forming  an  assemblage  of  hillocks  which  in  some  places  terminates 
in  a  southward-facing  cliff  and  in  others  ends  in  a  series  of  isolated  hillocks 
of  comparatively  shght  elevation.  In  two  or  three  places  the  schist 
formation  and  the  quartzite  formation  are  practically  in  contact,  being 
separated  by  a  distance  of  only  a  few  inches.  The  rock  on  the  south  side 
of  the  contact  plane  is  a  well-characterized  conglomerate.  It  is  exposed  in 
a  small  knoll  about  125  paces  long  and  50  paces  wide  at  1,400  paces  north 
and  1,350  paces  west  of  the  southeast  corner  of  the  section.  The  knoll  is 
practically  isolated  from  the  ledge  of  white  quartzite  to  the  south  and  the 
gneissoid-granite  ledges  to  the  north.  At  one  place  the  conglomerate  and 
granite  are  in  contact,  but  the  contact  line  is  so  short  and  the  relations 
between  the  two  rocks  are  so  obscure  that  nothing  can  be  learned  from  it. 
The  composition  of  the  conglomerate,  however,  is  such  that  no  doubt  can 
arise  as  to  its  meaning.  It  consists  largely  of  granite  and  gneiss  bowlders 
in  a  matrix  composed  of  the  debris  of  the  same  rocks. 

Falls  of  the  Sturgeon. — The  granites  and  quartzites  so  well  exposed  in 
the  western  half  of  sec.  8,  T.  39  N.,  E.  28  W.,  continue  eastward  in  almost 
unbroken  ledges  to  the  Sturgeon  River  and  a  short  distance  beyond.  Where 
the  river  crosses  them  occur  the  falls  and  the  gorge,  made  classic  by  the 
discussions  of  Credner,  Brooks,  Rominger,  Irving,  and  others.  The  falls 
are  over  granitoid  gneisses  (fig.  15).     Below  the  rapids  at  the  foot  of  the 


ALGONKIAN,  STURGEON  QUARTZITE.  197 

falls  is  an  open  basin  of  comparatively  smooth  water  flanked  on  both  sides 
by  conglomerates  and  arkoses,  and  below  this,  again,  is  a  narrow  rapids 
about  one-eighth  mile  long,  in  a  gorge  bordered  by  an  almost  unbroken 
ledge  of  heavily  bedded  white  quartzite,  striking  N.  65°  to  67°  W.,  and 
dipping  about  70°  to  80°  northeast.  There  is  a  fairly  good  trail  on  the 
east  side  of  the  river  that  runs  along  the  side  of  the  clifi"  at  about  20  feet 
above  the  water's  edge.  The  way  is  rough  and  broken,  but  the  trip  over 
the  trail  gives  an  excellent  opportunity  for  examining  the  walls  of  the 
gorge  on  both  sides  of  the  river.  Throughout  the  entire  length  of  the  gorge 
the  quartzite  is  of  the  same  general  character,  except  at  its  north  end. 
Here  the  rock  is  schistose  and  has  developed  in  it  a  considerable  quantity 
of  sericite,  in  this  respect  being  like  the  matrix  of  the  conglomerates  on  the 
contact  with  the  granite.  Everywhere  in  both  cliffs  the  quartzite  beds  are 
conformably  stratified,  no  indications  of  folding  being  observed  anywhere. 

It  will  be  remembered  that  Credner  described  the  conglomerates  as 
occurring  interbedded  with  micaceous  and  hornblendic  rocks.  He  mentions 
the  existence,  in  the  midst  of  the  granite-gneiss  series,  of  several  hundred 
feet  of  a  complex  consisting  of  thin-bedded  talcose  and  sandy  schists,  the 
latter  being  ripple  marked,  a  thin  layer  of  protogine- gneiss,  and  three  beds 
of  conglomerate,  each  30  feet  in  thickness,  in  which  were  found  pebbles  of 
gneiss,  granite,  and  quartzite  embedded  in  a  talcose  sandy  groundmass. 
The  conglomerate  was  thought  to  be  overlain  by  gneiss.  All  these  rocks 
he  regarded  as  Laurentian  (see  pp.  51-53). 

Brooks,  in  his  first  report,  described  the  same  conglomerates  and  the 
rocks  associated  with  them  as  a  series  of  soft,  light-gray,  talcose  slates, 
underlain  by  four  beds  of  conglomerate,  which  in  turn  are  underlain  by 
two  beds  of  protogine-gneiss  separated  by  a  bed  of  chlorite-schist.  Their 
precise  age  he  was  not  able  to  make  out,  though  he  declared  that  the 
conglomerates  separate  unquestionably  Laurentian  beds  from  those  that 
are  certainly  Huronian  (see  p.  58). 

In  his  second  report  he  described  the  sequence  at  the  falls  and 
concluded  that  "the  structural  facts,  in  connection  with  the  strong 
lithological  affinities  which  the  schist-conglomerate  series  bear  to  the 
Huronian,  and  the  still  more  important  fact  that  the  pebbles  contained  in 
the  conglomerate  are  unmistakably  Laurentian,  leave  no  question  in  my 
own  mind  but  that  the  rocks  under  consideration  are  Huronian  and  form 
the  base  of  the  series  at  this  point."     (See  pp.  66-67.) 


198  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Next  Rominger  described  the  succession  of  beds  in  the  vicinity  of 
the  falls  with  great  care.  The  conglomerate  he  described  as  having  a 
sericitic  schistose  matrix,  identical  with  certain  sericitie  schists  that  are 
interbedded  with  ripple-marked  feldspathic  beds.  These  he  thought  to 
be  in  "conformable  contiguity"  with  the  granites  to  the  north.  The 
author's  explanation  of  the  phenomena  is  given  in  the  following  words: 
"We  have  here,  evidently,  a  series  of  sedimentary  beds  deposited  on  a 
granitic  substratum,  which  during  the  upheaval  became  wedged  in  between 
the  plastic  granite  mass,  tilting  and  overlapping  them  locally  so  as  to 
appear  the  lower  beds"  (see  p.  75). 

Irving  corroborated  Brooks's  observations  concerning  the  nature  if 
the  conglomerate  and  agreed  with  him  as  to  its  signification.  He  found 
the  conglomerates  to  consist  of  granite  fragments  in  a  fine-grained  sericitic 
slaty  rock  which  at  times  looks  like  a  crystalline  schist.  The  granite  sheet 
described  by  Rominger  as  interleaved  with  the  conglomerates  could  not  be 
found.  The  character  of  the  rock  was  clear  evidence  to  Irving  that  "we 
have  here  to  do  with  a  detritus  derived  by  water  action  from  the  granitic 
and  gneissic  area  immediately  to  the  north.  The  slight  inclination  from 
the  vertical  toward  the  granite  which  these  conglomerate  schists  some- 
times show  is,  of  course,  no  argument  against  their  having  been  deposited 
upon  the  granite  as  a  substratuTU  "  (see  p.  94). 

A  careful  examination  of  the  rocks  exposed  along  both  sides  of  the 
gorge  below  the  falls  will  show  clearly  that  Brooks  and  Irving  are  correct 
in  their  conclusions.  Beginning  at  the  falls  and  passing  southward  on  the 
west  side  of  the  stream  we  find  at  the  falls  themselves  the  usual  granite- 
o-neiss  complex  cut  by  a  great  greenstone  dike,  which  forms  a  southward- 
facing  cUff,  at  the  base  of  which  is  a  small  patch  of  conglomerate.  South 
of  this,  across  a  valley  about  80  paces  wide,  we  next  find  a  schistose  seri- 
citic quartzite  which  passes  gradually  to  the  south  into  the  normal  white 
vitreous  quartzite  striking  N.  57°  W.  and  dipping  80°  to  83°  north. 

On  the  east  side  the  sequence  is  much  fuller.  We  have  again  at  the 
falls  a  mass  of  gneissoid  granite,  cut  by  greenstone,  forming  a  small 
clift'  at  whose  base  is  conglomerate.  The  banding  of  the  gneiss  strikes 
N.  80°  W.,  forming  an  acute  angle  at  its  contact  with  the  conglomerate. 
This  is  filled  with  fragments  and  bowlders  identical  in  character  to  the 
ffneiss  at  the  falls. 


ALGONKIAN,  STURGEON  QUARTZITE.  199 

South  of  the  conglomerate  is  a  narrow  bed  of  quartzite  followed  in 
succession  by  conglomerate,  fairly  massive  pink  arkose,  a  gray  micaceous 
quartzite  traversed  by  veins  of  red  feldspar,  and  another  bed  of  pink 
arkose,  the  whole  having  a  width  of  about  50  steps.  The  last  of  these  is 
well  exposed  on  the  north  side  of  the  wide  basin  below  the  contact.  For 
the  next  100  steps,  along  the  east  side  of  the  basin,  there  are  no  exposures, 
but  on  its  south  side  is  the  eastward  extension  of  the  light-gray  sericitic 
quartzite  already  mentioned  as  occurring  on  the  west  side  of  the  river. 
This  rock  forms  a  little  point  separating  the  larger  basin  below  the  falls 
from  a  smaller  one  still  farther  south.  On  the  east  side  of  this  southern 
basin  is  a  ledge  of  massive  greenstone,  and  on  its  south  side  is  the  northern 
edge  of  the  great  exposure  of  quartzite  which  stretches  about  300  paces 
southward.  The  strike  of  the  quartzite  is  N.  65°  W.  and  its  dip  70°  N. 
The  interbedded  quartzites  and  conglomerates  to  the  north  strike  N.  70°  W., 
and  dip  80°  N.     Their  schistosity,  on  the  other  hand,  strikes  N.  55°  E. 

There  can  nowhere  be  discovered  on  either  side  of  the  river  any  evi- 
dence of  the  existence  of  granite  beds  south  of  the  northernmost  exposure 
of  conglomerate.  All  of  the  rocks  south  of  this  point  are  unquestionably 
fragmental,  except,  of  course,  the  intrusive  greenstone,  and  all  of  them 
appear,  without  doubt,  to  have  been  derived  from  rocks  like  those  in  the 
granite-gneiss  complex.  In  the  ledge  some  of  the  arkoses  interstratified 
with  the  conglomerates  look  quite  like  fine-grained  gneisses,  but  in  thin 
section  under  the  mici'oscope  their  fragmental  character  is  very  plain  in 
spite  of  their  schistose  structure.  It  is  these  beds,  very  likely,  that  Credner 
regarded  as  gneisses  and  talcose  schists. 

The  conglomerate  grades  upward  through  the  arkoses  and  graywackes 
into  schistose  quartzite  and  through  these  into  the  massive  vitreous 
quartzite  of  the  gorge.  During  the  folding  of  the  series  readjustments  took 
place  along  a  zone  bordering  the  contact  with  the  underlying  granites  and 
as  a  result  of  the  consequent  shearing  we  find  the  conglomerates  and  othei 
rocks  near  the  base  of  the  series  schistose,  while  the  quartzites  at  a  greater 
distance  from  this  contact  are  practically  massive.  Moreover,  at  the  lower 
horizon  the  series  consists  of  several  kinds  of  beds  varying  in  hardness  and 
rigidity,  whereas  the  quartzites  comprise  a  set  of  beds  of  the  same  kind. 
It  is  a  well-recognized  fact  that  readjustments  during  the  process  of  folding 
are  much  more  apt  to  take  place  between  beds  of  different  charactei's  than 
in  a  sei'ies  of  uniform  character. 


200  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

RANDVILLE  DOLOMITE. 

Next  in  order  above  the  Sturgeon  quartzite  is  a  thick  series  of  beds 
among  which  dohjmitic  layers  predominate.  This  series  is  identical  in 
character  with  a  similar  series  in  the  Felch  Mountain  district  known  as  the 
Randville  dolomite.  It  is,  raorever,  in  the  same  geological  position  as  the 
latter,  and  hence  is  regarded  as  its  continuation  into  the  Menominee  district. 
It  has  therefore  been  designated  by  the  same  name. 

DISTRIBUTION  AND  TOPOGRAPHY. 

The  Randville  dolomite  occupies  three  separate  belts,  whose  positions 
and  shapes  are  determined  by  the  folding  to  which  the  formation  has  been 
subjected.  These  will  be  referred  to  as  the  northern,  central,  and  southern 
belts  of  dolomite. 

THE    NORTHERN    BELT. 

The  northern  belt  lies  immediately  south  of  the  belt  of  Sturgeon 
quartzite,  and  presumably  along  nearly  its  entire  extent  from  sec.  3,  T.  40 
N.,  R.  30  W.,  to  sec.  8,  T.  39  N.,  R.  28  W.  Only  a  few  exposures  have 
been  seen,  but  they  are  widely  distributed  through  the  area.  The  eastern- 
most one  is  a  calcareous  or  dolomitic  quartzite  outcropping  on  the  south 
bank  of  the  Sturgeon  River  a  few  hundred  paces  south  of  the  center  of  sec. 
8,  T.  39  N.,  R.  28  W.  It  is  an  obscure  ledge,  almost  hidden  by  the  sandy 
detritus  produced  by  its  disintegration.  The  next  western  exposures 
discovered  are  located  in  a  swamp,  about  400  paces  south,  200  paces  east 
of  the  north  quarter  post,  sec.  33,  T.  40  N.,  R.  29  W.  This  location  is  5^ 
miles  distant  from  the  first  ledge.  The  exposures  are  two  in  number,  but 
they  are  so  close  together  that  they  may  be  considered  as  parts  of  a  single 
one.  The  rock  is  a  friable  quartzite  with  a  carbonate  cement,  interbanded 
with  a  few  cherty  layers.  The  third  group  of  ledges  is  in  the  southeast 
quarter  of  sec.  11  and  the  northeast  quarter  of  sec.  14,  in  T.  40  N.,  R.  30  W. 
It  comprises  five  independent  exposures  outcropping  from  the  sides  of  the 
valley  of  the  little  stream  that  empties  into  Pine  Creek  at  Hamilton  and 
Merryman's  camp  No.  6,  near  the  line  between  sees.  11  and  14,  T.  40  N., 
R.  30  W.  They  extend  in  a  line  running  about  southeast  for  800  feet, 
thus  giving  a  good  section  across  the  formation.  A  dolomitic  mai'ble  and 
dolomitic  quartzite  constitute  the  northern  ledges,  crystalline  dolomites  the 
intermediate  ones,  and  cherts  the  southernmost  one.     The  fourth  and  last 


ALGONKIAN,  RANDVILLE  DOLOMITE.  201 

exposure  belong-ing  in  this  belt  is  that  ah-eady  referred  to  as  occurring  in 
the  northeast  quarter  sec.  3,  T.  40  N.,  R.  30  W.  (see  p.  193). 

In  the  country  between  these  groups  of  exposures  no  ledges  of  any 
kind  have  been  discovered,  but  a  pit  in  the  northeast  quarter  of  the  south- 
west quarter  of  sec.  7,  T..39  N.,  R.  28  W.,  and  several  drill  holes  farther 
west  (see  p.  405)  encountered  cherty  quartzites  and  dolomites  belonging  to 
the  formation  north  of  the  jaspers  and  ores  of  the  Appleton  location.  It  is 
probable  that  the  formation  continues  uninterruptedly  between  its  known 
occurrences,  except  for  a  possible  break  in  sec.  34,  T.  40  N.,  R.  29  W., 
The  whole  belt  with  this  exception  has  therefore  been  colored  for  the  forma- 
tion on  the  maj)  (PI.  IX).  It  is  quite  possible,  however,  that  in  the 
intervals  between  the  ledges  erosion  has  carried  away  the  dolomite  and 
that  the  Upper  Huronian  rests  immediately  upon  the  Sturgeon  quartzite. 
The  mapping  of  sec.  34,  T.  40  N.,  R.  29  W.,  is  in  accordance  with  this 
view. 

The  country  underlain  by  the  northern  belt  of  dolomite  is  now  the  val- 
ley of  Pine  Creek.  It  is  a  low  plain,  covered  by  sand,  which  has  been 
partly  deposited  by  the  creek  and  partly  by  glaciers.  It  was  a  valley  long 
Viefore  the  advent  of  the  glaciers,  and  there  is  some  evidence  indicating  that 
there  was  a  valley  in  this  place  even  before  the  deposition  of  the  Cambrian 
sandstone.  The  long-continued  erosion  produced  by  Pine  Creek  and  its 
ancestors  has  reduced  the  area  to  one  of  low  relief  The  topography  is 
very  different  in  character  from  that  of  the  other  dolomite  areas  in  the  dis- 
trict, which  correspond  to  divides,  and  thus  are  elevations  rather  than 
depressions. 

THE    CENTRAL   BELT. 

The  central  belt  of  dolomite  borders  the  north  side  of  Lake  Antoine 
for  a  portion  of  its  length,  passes  eastward  between  the  Cuff  and  the  Indiana 
mines  and  north  of  the  Forest  mine,  and  terminates  at  the  bluff  known  as 
Iron  Hill  in  the  northeast  quarter  of  sec.  32,  T.  40  N.,  R.  29  W.  The  belt 
is  well  marked  in  places  by  numerous  and  often  large  exposures,  but,  as  in 
the  area  just  described,  the  exposures  are  not  continuous.  The  intervals 
between  them  are  sometimes  covered  by  deep  deposits  of  soil,  but  more 
frequently  they  are  occupied  by  the  Lake  Superior  sandstone,  which  com- 
pletely blankets  the  underlying  rocks.  Fortunately,  however,  there  has 
been  some  exploratory  work  done  along  the  belt,  and  this  has  shown  in 


\ 

202  THE  MENOMINEE  IRON-BEAKING  DISTRICT. 

several  places  the  existence  of  the  dolomite  beneath  the  surface.  Conse- 
quenth"  on  the  map  the  color  of  the  dolomite  formation  is  made  to  cover 
a  continuous  belt  from  the  known  westernmost  occurrence  of  the  rocks 
belonging-  in  it  to  the  easternmost  known  occurrence  at  Iron  Hill. 

The  known  occurrences  of  the  dolomite  and  other  rocks  belonging  to 
the  formation  along  this  belt  are  as  follows:  A  tunnel  and  drill  hole  near 
the  quarter  post  between  sees.  20  and  21,  T.  40  N.,  R.  30  W.,  which  runs 
north  into  the  hill  for  a  distance  of  about  800  feet  all  in  dolomite;  a  group 
of  bluifs  stretching  for  about  one-half  mile  through  the  southeast  quarter  of 
sec.  21  and  the  southwest  quarter  of  sec.  22,  T.  40  N.,  R.  30  W.,  and  a  test 
pit  in  chert  just  south  of  these;  a  "horse"  of  white  dolomite  in  the  first  level 
of  the  Cuff  mine;  a  small  ledge  of  the  same  rock  on  the  south  side  of  the 
track  of  the  Escanaba  and  Iron  Mountain  Railroad  (Chicago  and  North- 
western) about  1,000  feet  east  of  the  north  quarter  post  of  sec.  27,  T.  40  N., 
R.  30  W.;  dolomites  and  red  slates  in  the  shaft  of  the  Federal  exploration 
near  the  southeast  corner  of  sec.  22  in  the  same  town;  dolomites  and  red 
slates  in  the  drill  holes  near  the  Indiana  mine,  and  in  the  workings  of  this 
mine;  red  calcareous  slates  in  the  dump  piles  of  two  test  pits  on  the  north 
side  of  the  Escanaba  and  Iron  Mountain  Railroad  track  near  the  line 
between  sees.  26  and  27,  T.  40  N.,  R.  30  W.;  two  ledges  of  dolomite  a 
short  distance  west  of  the  Forest  mine  near  the  center  of  sec.  25,  T.  40  N., 
R.  30  W.;  one  ledge  and  a  pit  exposing  the  same  rock  near  the  center  of  the 
southeast  quarter  of  this  section;  and,  finally,  the  numerous  large  exposures 
running  through  the  east  half  of  sec.  32,  T.  40  N.,  R.  29  W. 

The  only  stretches  of  any  considerable  length  over  which  the  formation 
is  shown  on  the  map  without  direct  evidence  of  its  existence  beneath  the 
surface  are:  (1)  The  three-fourths  of  a  mile  between  the  west  line  of  sec. 
21,  T.  40  K.,  R.  30  W.,  and  the  road  to  Hamilton  and  Men-yman's  camp, 
which  runs  through  the  center  of  the  southeast  quarter  of  this  section; 
and  (2),  the  2J  miles  between  the  west  line  of  sec.  23,  in  the  same 
town,  and  the  exposures  ne'ai-  the  Forest  mine  in  the  eastern  portion 
of  the  southwest  quarter  of  sec.  25,  T.  40  N.,  R.  30  W.;  and  (3),  the  IJ 
miles  between  the  exposures  in  the  southeast  quarter  of  the  last-named 
section  and  those  in  the  center  of  sec.  32  in  the  town  east. 

In  these  intervals  the  surface  rock  is  the  Lake  Superior  sandstone. 
This  occupies  most  of  the  areas  between  the  known  dolomite  occurrences, 


ALGONKIAN,  KANDVILLE  DOLOMITE.  203 

and,  together  with  the  drift  covering,  prevents  access  to  the  underlying 
Huronian  rocks.  The  sandstone,  however,  lias  been  test-pitted  in  many 
places,  and  in  the  bottoms  of  the  pits  the  rock  is  often  discovered  to  be  a 
conglomerate  containing  many  bowlders  of  dolomite  and  dolomitic  chert, 
or  light-colored  sandstone  containing  an  abundant  dolomitic  cement.  In 
either  case  the  inference  is  strong  that  the  dolomite  is  near  at  hand.  Conse- 
quently the  Randville  formation  is  mapped  as  underlying  the  sandstone  in 
these  places. 

The  belt  as  outlined  by  these  exposures  is  not  known  to  be  wider  than 
about  870  feet  at  any  point.  This  width  is  reached  at  its  eastern  end,  at 
Iron  Hill,  and  north  of  the  Indiana  mine.  For  a  mile  west  of  the  Indiana 
mine  it  has  a  width  of  not  more  than  400  feet,  but  again,  in  the  tunnel  near 
the  west  line  of  sec.  21,  its  known  width  is  said  to  be  800  feet.  As  a  mat- 
ter of  fact,  neither  the  northern  nor  the  southern  border  of  the  belt  is  well 
defined  for  any  great  distance.  At  Iron  Hill,  at  the  Forest  and  at  the 
Indiana  mines,  the  position  of  its  southern  border  is  known,  and  for  a  mile 
west  of  the  last-named  mine  it  is  knt)wn  with  close  approximation  to  the 
truth.  But  only  at  the  Cuff  mine  has  its  northern  boundary  been  disclosed. 
Elsewhere  it  is  buried  under  the  Lake  Superior  sandstone. 

The  belt  is  so  narrow  that  it  has  produced  little  effect  on  the  topog- 
raphy. Through  most  of  its  extent  it  appears  at  or  near  the  base  of  the 
southern  slopes  of  a  ridge  of  high  hills  formed  of  the  Cambrian  sandstone. 
Near  the  Cuff  mine  and  at  Iron  Hill,  the  ledges  of  the  formation  appear  as 
small,  isolated  knolls  or  they  are  grouped  together,  forming  little  plateaus 
with  steep  southern  escarpments,  their  northern  escarpments  being  buried 
under  the  overlying  sandstone. 

THE    SOUTHERN   BELT. 

DISTKIHUTION. 

The  southern  and  most  important  belt  of  dolomite  extends  all  the  way 
from  the  western  side  of  Prospect  Bluff,  west  of  Iron  Mountain,  to  the 
village  of  Waucedah,  at  the  eastern  end  of  the  area  mapped.  Where  not 
exposed  at  the  surface  the  rock  has  been  found  in  mines  and  test  shafts  and 
pits,  so  that  there  is  a  reasonable  certainty  that  it  exists  throughout  this 
distance  of  16  miles.  Where  theie  is  any  doubt  of  its  existence  this  is  due 
to  a  considerable  thickness  of  overlying  Lake  Superior  sandstone. 


204 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


The  westernmost  exposure  is  near  the  Hamilton  mine  in  the  southwest 
quarter  of  sec.  30,  T.  40  N.,  R.  30  W.,  but  the  rock  has  been  met  with  in 
underground  workings  of  exploration  shafts  as  far  west  as  the  center  of 
sec.  25  in  T.  40  N.,  R.  31  W.  (See  fig.  16.)  From  the  Hamilton  mine  east- 
ward the  belt  is  well  marked  by  numerous  and  often  large  exposures  and  by 
ledges  discovered  in  exploratory  and  mining  operations  as  far  as  the  northeast 
quarter  of  sec.  18,  T.  39  N.,  R.  28  W.  Beyond  this  the  country  is  destitute 
of  exposures,  but  about  1,175  paces  north,  600  paces  west  of  the  southeast 
comer  of  sec.  17,  T.  39  N.,  R.  28  W.,  there  is  a  small  pit  in  the  dump  of 
which  are  many  fragments  of  pink  dolomite.  No  direct  evidence  of  the 
contiimatiou  of  the  belt  beyond  this  point  is  at  hand,  since  the  workings  of 

S  9  7     _N 


Brier  slate 


Curry  member  q,  ^ 

Ore 
conglomerate 


Fig.  16. — Cross  section  tlirough  pits  and  shafts  near  the  center  of  sec.  'Irt,  T.  40  N.,  R.  31  W. 

the  Breen  and  Emmett  mines  have  not  penetrated  below  the  iron  formation, 
and  the  explorations  north  of  these  mines  have  nowhere  exposed  the  i-ocks 
lying  beneath  the  Cambrian  sandstone.  That  the  belt  continues  eastward 
uninterruptedly  through  sees.  18,  17,  and  16,  T.  39  N.,  R.  28  W.,  is,  how- 
ever, rendered  probable  by  the  fact  that  two  magnetic  lines  that  have 
their  origin  in  sec.  18,  one  just  north  of  known  exposures  of  the  dolomite 
and  the  other  to  the  south  of  them,  can  be  traced  without  break  into  sec.  15 
of  this  township.  These  indicate  that  the  iron  formation  continues  eastward 
this  far,  and  since  the  dolomite  is  immediately  beneath  the  iron  formation, 
the  inference  is  fair  that  the  dolomite  also  continues  to  the  same  distance. 
The  belt  occupies  a  narrow  strip  of  country  running  a  little  south 


ALGONKIAN,  RANDVILLE  DOLOMITE.  205 

of  east  through  the  southern  portions  of  sees.  23  and  24,  and  the  northern 
parts  of  sees.  26  and  25,  T.  40  N.,  R.  31  W.,  and  through  the  whole  or 
parts  of  sees.  30,  29,  28,  27,  31,  32,  33,  34,  35,  and  36,  T.  40  N.,  R.  30  W.; 
sees.  2  and  1,  T.  39  N.,  R.  30  W.;  sees.  6,  5,  4,  3,  9,  10,  11,  and  12,  T.  39 
N.,  R.  29  W.;  and  sees.  7,  18,  17,  and  16,  T.  39  N.,  R.  28  W. 

The  northern  boundary  of  the  belt  is  in  general  very  indefinite.  At 
several  places  it  can  be  fairl}^  well  determined  by  exposures,  viz,  just  north 
of  the  island  in  Lake  Antoine  and  south  of  the  Loretto  mine,  in  see.  7,  T. 
39  N.,  R.  28  W.,  but  elsewhere  it  can  not  be  definitely  fixed  without 
recourse  to  test  pits  and  shafts,  because  it  is  deeply  buried  under  the 
drift  or  is  covered  by  thick  deposits  of  the  Cambrian  sandstone.  As 
nearlj-  as  can  be  determined  this  northern  boundary  is  about  as  follows: 
Beginning  at  the  Menominee  River,  near  the  east-west  quarter  line  of  sec.^ 
23,  T.  40  N.,  R.  31  W.,  it  runs  a  little  south  of  east  to  the  southwest  shore 
of  Lake  Antoine  where  it  is  crossed  by  the  east  line  of  sec.  30,  T.  40  N.,  R. 
30  W.  Here  it  is  reported  to  have  been  found  beneath  the  surface  in  di'ill 
holes.  From  this  point  it  continues  to  the  soutlieast  shore  of  the  lake, 
passing  just  north  of  the  island  and  the  little  knoll  opposite  its  east  end. 
It  is  mapped  as  passing  around  this  knoll  and  running  west  for  a  short 
distance,  then  turning  eastward  again  and  continuing  its  south-of-east 
course  to  a  point  in  the  northwest  quarter  of  the  southeast  quarter  of  sec. 
35,  T.  40  N.,  R.  30  W.  The  reentrant  on  the  southeast  shore  of  Lake 
Antoine  is  based  solely  on  topography.  On  the  little  knoll  east  of  the 
island  the  dolomite  is  well  exposed.  It  is  known  by  test  pits  to  occur 
under  the  sandstone  nearly  to  the  base  of  the  northern  slope  of  the  large 
hill  to  the  south.  Between  this  hill  and  the  knoll  is  a  narrow  valley  and  a 
swamp.  The  contrast  between  it  and  the  hills  on  both  sides  is  noticeable. 
Since  similar  low  ground  elsewhere  is  known  to  be  undeidain  by  slates,  the 
assumption  is  made  that  this  valley  is  likewise  carved  from  these  rocks,  and 
the  dolomite  is  mapped  as  passing  around  it.  From  the  ijoint  in  the  south- 
east quarter  of  sec.  35,  the  boundary  is  again  supposed  to  make  a  reentrant 
to  the  west  to  correspond  to  the  known  salient  at  Quinnesec  on  the  south 
side  of  the  belt.  From  the  end  of  the  reentrant  the  line  is  drawn  straight 
to  about  the  center  of  the  southeast  quarter  of  see.  3,  T.  39  N.,  R.  29  W. 
Except  at  its  eastern  portion  the  boundary  here  is  conjectural.  Drill  holes 
have  shown  the  existence  of  dolomite  near  the  north  line  of  the  southwest 


206  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

quarter  of  tlie  southeast  quarter  of  sec.  35,  T.  40  N.,  R.  30  W.,  and  near  the 
northeast  corner  of  sec.  2,  T.  39  N.,  R.  30  W.,  and  a  pit  exposes  it  500  paces 
east  of  this  corner  in  sec.  1.  To  the  east  no  ledges  of  any  rock  okler  than 
the  sandstone  are  met  until  the  southeast  quarter  of  sec.  3,  T.  39  N.,  R. 
29  W.,  is  reached.  Here  there  is  a  single  small  ledge  of  contorted  dolo- 
mite, with  its  folds  apparently  pitching  flat  to  the  west.  The  boundary 
line  is  made  to  pass  around  this  ledge,  then  to  pass  southwestvvard  to  the 
center  of  the  southeast  quarter  of  the  southeast  quarter  of  sec.  4  and  to  turn 
once  more  to  the  east,  forming  a  reentrant  to  correspond  to  the  dolomite 
salient  on  the  south  side  of  the  belt  between  the  Norway  and  the  Aragon 
mines.  From  the  apex  of  this  reentrant  the  boundary  line  is  again  drawn 
straight  to  about  the  east  quarter  post  of  sec.  11,  T.  39  N.,  R.  29  W.  Here 
it  turns  northwest  to  a  point  500  paces  north  of  the  center  of  this  section 
and  then  eastward  again  skirting  the  north  side  of  the  dolomite  ridges  that 
stretch  in  almost  a  continuous  line  from  this  point  to  another  just  south  of 
the  Appletou  mine,  in  sec.  7,  T.  39  N.,  R.  28  W.  The  eastward-extending 
embay ment  is  necessitated  by  the  presence  of  13  or  more  pits  in  slates 
stretching  along  the  north-south  center  line  of  the  southwest  quarter  of  the 
northeast  quarter  of  sec.  11.  The  boundary  is  as.sumed  to  be  very  near 
the  northernmost  ledges  in  sees.  11  and  12,  T.  39  N.,  R.  29  W.,  because  of 
the  marked  change  in  the  topography  noted  here.  The  area  to  the  south, 
known  to  be  underlain  by  dolomite,  possesses  an  undulating  surface  broken 
by  numerous  ledges,  ridges,  and  hillocks  of  rock,  while  that  to  the  north 
is  a  low,  flat,  swampy  country  in  which  no  ledges  of  -Any  kind  are  exposed. 
The  continuation  of  the  boundary  eastward  to  the  point  where  the  belt  is 
lost  under  the  thick  covering  of  Paleozoic  sediments  that  stretch  from  the 
eastern  end  of  the  Menominee  trough  to  Lake  Michigan,  is  placed  at  a 
uniform  distance  south  of  the  magnetic  line  that  begins  a  little  west  of  the 
Loretto  mine  and  is  traced  with  fairly  good  success  to  about  the  center  of 
sec.  15,  T.  39  N.,  R.  28  W. 

It  will  be  noted  that  the  evidence  with  respect  to  the  position  of  the 
northern  border  of  the  dolomite  belt  is  mainly  negative.  There  are  no 
exposures  north  of  the  dolomite  and  near  it  that  determine  the  limit  of  the 
belt  in  this  direction.  The  boundary  line  is  drawn  close  to  the  northern- 
most ledges  of  the  dolomite  where  such  ledges,  as  indicated  by  the  topog- 
raphy, are  plainly  near  the  north  side  of  the  belt.     Between  such  ledges 


ALGONKIAN,  RANDVILLE  DOLOMITE.  2(»7 

the  boundary  is  drawn  straight  except  where  sinuosities  are  clearly  indicated 
by  their  existence  in  the  south  boundary.  In  these  cases  it  is  assunied  that 
the  belt  is  folded  throughout  its  entire  breadth  and  that  these  folds  must 
find  expression  at  its  northern  boundary.  The  only  sinviosity  in  the  north 
boundary  indicated  by  the  occurrence  of  rocks  other  than  those  belonging 
in  the  dolomite  series  is  that  extending  southeastward  into  sec.  11,  T.  39  N., 
R.  29  W.,  and  this  is  indicated  only  b)^  a  row  of  very  old  test  pits,  on  the 
dumps  of  which  slates  have  been  found.  The  country  near  this  northern 
boundary  has  not  been  explored  anywhere  to  a  depth  sufficient  to  reach 
the  rocks  underlying  the  sandstone  except  by  the  pits  in  sec.  11.  Natural 
exposures  of  other  rocks  are  unknown.  From  the  foregoing  it  is  clear  that 
the  position  of  the  northern  boundary  of  the  dolomite  must  of  necessity  be 
largely  conjectural. 

The  southern  boundary,  on  the  other  hand,  is  rather  sharply  delim- 
ited, not  merely  by  exposures,  but  also  by  the  undergi-ound  workings 
of  many  of  the  mines.  The  evidence  is  so  uniformly  distributed  along 
the  entire  belt  that  there  can  be  but  little  doubt  that  this  boundary  is 
very  near  the  position  at  which  it  is  mapped.  The  only  portions  of  the 
boundary  that  may  be  considered  doubtful  are  (1)  the  2^  miles  between 
the  Menominee  River  and  the  old  Ludington  mine,  600  paces  west  of  the 
east  line  of  sec.  25,  T.  40  N.,  R.  31  W.,  and  (2)  the  3^  miles  between  the 
center  of  sec.  18,  T.  39  N  ,  R.  28  W.,  and  the  east  line  of  sec.  15  in  the 
same  town.  Along  the  belt  of  the  iron  formation  between  the  Menominee 
River  and  the  old  Ludington  mine  test  pits  have  been  dug,  and  from  some 
of  these  drifts  have  been  run  to  the  north.  In  only  one  case,  viz,  near  the 
center  of  sec.  25,  T.  40  N.,  R.  31  W.  (see  fig.  16),  was  any  dolomite  met 
with,  but  in  several  instances  drifts  and  drill  holes  penetrated  rock  that 
indicates  the  close  proximity  of  the  dolomite  formation.  A  drill  hole  put 
down  vertically  about  1,000  feet  east  and  420  feet  north  of  the  west 
quarter  post  of  sec.  25  penetrated  a  cherty  quartzite  that  is  usually  found 
at  the  top  of  the  dolomite  formation.  At  other  places  the  dump  heaps  show 
slaty  rocks  that  are  usually  found  near  the  dolomite,  but  at  onlv  the  two 
points  referred  to  above  is  there  certain  evidence  that  the  southern  contact 
of  the  dolomite  is  very  near.  At  the  eastern  end  of  the  district  the  evi- 
dence used  in  delineating  the  southern  boundary  of  the  belt  is  the  same  as 
that  used  in  fixing  its  northern  boundary.     A  magnetic  line  extends  from 


208  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

sec.  18,  T.  39  N.,  R.  28  W.,  continuously  to  the  Breen  mine.  In  sec. 
18  the  southern  boundary  of  tlie  dolomite  is  a  short  distance  north  of  this 
line.  The  relative  position  of  the  dolomite  and  the  magnetic  line  is  assumed 
to  be  the  same  to  the  east,  and  the  mapping  is  in  accordance  with  this  view. 
At  Waucedah  there  is  no  definite  magnetic  line,  but  there  are  numerous 
test  pits  nortli  of  the  village  by  which  the  existence  of  the  lowermost  mem- 
ber of  the  iron  formation,  with  a  steep  dip  to  the  south,  is  well  established. 
Since  the  dolomite  elsewhere  lies  just  under  this  formation,  its  southern 
boundary  at  Waucedah  is  placed  at  a  distance  north  of  the  southern  bound- 
ary of  the  northernmost  member  of  the  iron  formation  corresponding  to  the 
average  width  of  this  formation  in  those  places  where  its  dip  is  nearly 
vertical. 

In  the  14  miles  between  sec.  25,  T.  40  N.,  R.  31  W.,  and  sec.  18,  T.  39 
N.,  R.  28  W.,  as  has  been  said,  the  evidence  that  fixes  the  position  of  the 
dolomite  belt  is  conclusive.  The  nature  of  this  evidence  need  not  be 
referred  to  here,  as  it  is  discussed  rather  fully  in  connection  with  the 
description  of  the  iron-bearing  Vulcan  formation.  The  evidence  is  exhib- 
ited on  the  maps  showing  the  disti'ibution  of  the  rocks  in  the  neighbor-" 
hood  of  the  various  mines. 

TOPOORAPHY. 

From  the  Menominee  River  as  far  east  as  the  Sturgeon  River  the  country 
underlain  by  the  dolomite  is  a  range  of  high  hills  (PI.  XIII,  B),  broken  only 
at  Iron  Mountain,  at  Quinnesec,  at  Norway,  and  at  the  Sturgeon  River  by 
north-south  gaps.  The  slopes  of  the  ridge  are  comparatively  steep  on  both 
the  north  and  the  south  sides,  but  the  northern  slope  usually  merges  grad- 
ually into  the  plains  lying  at  its  base,  while  the  southern  slope  in  some 
places  terminates  in  little  precipices,  well  seen  east  of  Quinnesec  along  the 
north  side  of  the  wagon  road  leading  to  Norway  (PI.  XV,  A).  These 
precipices  are  rough  and  rugged  masses  of  dolomite  (PI.  XV,  B)  or  cherty 
quartzite  rising  suddenly  out  of  a  plain  underlain  by  slates.  Their  exist- 
ence is  due  to  differential  weathering,  the  slates  having  been  eroded  much 
more  rapidly  than  the  resisting  dolomite.  Where  the  dolomite  is  bordered 
on  the  south  by  the  iron  formation  the  slope  is  gradual,  the  dolomite 
occupying  its  upper  portion  and  the  iron-bearing  rocks  its  lower  portion. 

While  the  existence  of  the  ridge  is  no  doubt  due  to  the  presence  of  the 


U.   S.   GEOLOGICAL   SURVEY 


MONOGRAPH    XLVI      PL.    XV 


A      VIEW   OF    DOLOMITE   BLUFFS   ON    NORTH    SIDE   OF    HIGHWAY    FROM    QUINNESEC  TO    NORWAY. 

Near  point  where  stream  crosses  road  in  sec.  2,  T.  39  N.,  R.  30  W. ;  about  one-fourth  mile  east  of  Quinnesec.  The  cliffs  are  composed  of  nearly 
vertically  bedded  Randville  dolomite,  traversed  by  thin  seams  of  chert  parallel  to  bedding.  The  plain  at  the  base  of  the  cliffs  is  underlain 
by  Hanbury  slate.     The  view  gives  some  idea  of  the  rough  topography  produced  by  the  weathering  of  the  dolomite, 


B.      NEARER   VIEW    OF    DOLOMITE   BLUFF   SHOWN    IN    A. 
The  rough  character  of  the  topography  is  very  apparent  in  this  view. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  209 

dolomite,  its  present  height  is  determined  partly  by  the  horizontal  Lake 
Superior  sandstone,  which  caps  it  almost  universally,  and  gives  it  an  even 
or  gently  undulating  sky  line.  Where  the  sandstone  is  lacking,  i.  e.,  on 
the  lower  portions  of  the  ridge,  the  dolomite  outcrops  in  small,  isolated  hil- 
locks and  groups  of  ledges.  Tlie  former  are  somethnes  very  steep  on  all 
sides,  and  exceeding-ly  rugged;  at  other  times  they  are  long,  narrow,  low 
ridges  with  gently  sloping  sides  and  smooth,  rounded  tops.  In  a  few  places 
the  rock  forms  low  ledges  rising  only  a  few  inches  above  the  general  sur- 
face. Between  the  exposures  are  deposits  of  drift.  The  differences  in  the 
character  of  the  topography  underlain  by  the  dolomite  seem  to  depend 
largely  on  the  completeness  with  which  the  glacial  sands  have  been  removed. 
If  it  could  all  be  removed  from  above  the  dolomite  the  country,  except 
where  covered  by  sandstone,  would  be  extremely  rough. 

What  is  true  of  the  present  tojjography  of  this  area  is  true  also  of  its 
pre- Potsdam  surface.  Mining  operations  in  several  instances  have  uncovered 
the  sandstone  at  considerable  depths  beneath  the  present  surface.  In  some 
cases  the  rock  seems  to  fill  old  gorges  cut  through  the  dolomite;  in  other 
cases  it  rests  against  ancient  dolomite  precipices,  and  in  still  other  instances 
it  can  be  seen  to  rest  upon  shelving  shores,  built  of  this  material  It  is  also 
probable  that  the  transverse  gaps  referred  to  as  crossing  the  dolomite  ridge 
at  Iron  Mountain,  Quinnesec,  and  Norway  were  once  filled  with  sandstone. 
While  there  is  by  no  means  sufficient  data  from  which  to  reconstruct  the 
old  topography,  it  is  very  clear  that  the  ancient  dolomite  surface  was  more 
rugged  than  its  present  surface.  Moreover,  since  the  sandstone  is  found  at 
much  lower  levels,  both  north  and  south  of  the  ridge,  than  its  basal  layers 
on  the  ridge,  it  is  further  plain  that  the  dolomite  ridge  was  in  existence  in 
pre-Potsdam  time,  and  that  its  elevation  above  the  surrounding  surface  was 
then  not  greatly  different  from  its  elevation  to-day. 

LITHOLOGY. 

The  Randville  dolomite  consists  of  a  series  of  beds  in  which  dolomitic 
layers  predominate.  With  the  pure  dolomites  are  associated  quartzose 
dolomites,  dolomitic  quartzites,  argillaceous  dolomites,  dolomitic  slates, 
cherty  quarzites,  and  talcose  schists.  Besides  these  there  are  present 
locally,  particularly  near  the  ends  of  folds  and  along  contact  zones,  dolo- 
mitic breccias  and  conglomerates  and  cherty  quartz  breccias. 

MON    XLVI — 04 14 


210  THE  MENOMINEE  IRON-BEARING  DISTRICT. 


DOLOMITE    AND   DOLOMITIC   SANDSTONES. 


The  predoininant  rock  of  the  series  is  an  ahiiost  massive,  apparently 
homogeneous,  fine-grained  white,  pink,  blue,  or  buff  dolomite,  occurring  in 
beds  from  a  few  inches  to  many  feet  in  thickness.  In  a  few  places  the  rock 
is  a  white  coarsely  crystalline  marble,  a  phase  well  seen  in  the  ledge  400 
paces  west  of  the  northeast  corner  of  sec.  14,  T.  40  N.,  R.  30  W. 

The  lighter-colored,  purer  dolomites  weather  with  smooth  white  or 
very  light-pink  or  light-blue  surfaces  that  are  crossed  here  and  there  by 
thin  projecting  seams.  Oftentimes  the  projecting  bands  are  parallel  to  the 
bedding-,  when  they  are  found  to  be  composed  of  dolomitic  quartzite 
interbedded  with  the  purer  dolomite.  In  other  cases  the  projecting  bands 
anastomose  or  run  irregularly  over  the  weathered  surfaces,  often  intersect- 
ing the  bedding  planes  of  the  rock  at  acute  angles.  These  seams  are 
plainly  narrow  veins  of  quartz.  Their  abundance  proves  clearly  that  the 
dolomites,  in  spite  of  their  homogeneous  appearance,  have  been  extensively 
fractured  and  crushed. 

The  weathered  surfaces  of  the  darker-colored  dolomites  are  covered 
with  a  thin  layer  of  light-brown  sandy  substance  varying  in  thickness  from, 
a  fraction  of  a  millimeter  to  several  millimeters,  which  indicates  the 
presence  of  iron  in  the  carbonate,  and  the  existence  of  quartz  grains  inter- 
mingled with  the  dolomite.  At  one  place  nodular  weathering  was  observed. 
This  was  in  tlie  large  ledge  underlying  the  Lake  Superior  sandstone  in  the 
quarry  in  the  southwest  quarter  of  the  southeast  quarter  of  sec.  30,  T.  40 
N.,  R.  30  W.  Here  the  dolomite  strikes  regularly  N.  75°  W.,  and  dips 
78°  N,  and  on  its  eroded  edges  the  sandstone  lies  horizontal.  Near  the 
contact  of  the  two  rocks,  the  dolomite  is  filled  with  nodules  that  differ 
slightly  in  color  from  the  surrounding  matrix  and  thus  produce  a  rock 
strongly  resembling  in  appearance  a  conglomerate.  No  difference  can  be 
detected  between  the  texture  of  the  nodules  and  that  of  the  cementing 
material.  The  nodules  are  slig'htly  harder  than  the  rock  in  which  they  lie 
and  perhaps  they  contain  a  small  percentage  of  silica  leached  from  the 
overlying  sandstone. 

While  man}'  of  the  dolomite  beds  in  the  Randville  series  are  practically 
pure  dolomites,  others  contain  a  large  admixture  of  sand  grains.  In  some 
cases  dolomite  is  in  excess,  in  others  the  principal  component  is  sand  with 


ALGONKIAN,  RANDVILLE  DOLOMITE.  211 

dolomite  as  a  sparse  cement.  The  former  have  been  (;alled  quartzose  dt)ki- 
mites  and  the  hitter  dolomitic  sandstones.  These  rocks  occur  in  beds  from 
a  few  inches  to  20  or  more  feet  in  thickness  at  various  horizons  in  the  series, 
but  more  frequently  near  its  bottom  than  elsewhere.  The  basal  beds, 
which  are  gradational  in  character  between  the  underlying  Sturgeon  quartz- 
ite  and  the  overlying  dolomitic  phases  of  the  Randville  series,  are  almost 
exclusively  dolomitic  sandstone.  On  the  fracture  surfaces  of  fresh  specimens 
of  the  quartzose  dolomites  the  quartz  appears  as  small,  round,  glistening 
spots  against  a  dull  groundmass  of  gray,  white,  or  bluish  dolomite.  The 
grains  are  so  evenly  distributed  through  the  carbonate  that  at  a  hasty  glance 
many  specimens  resemble  oolitic  limestones.  In  the  most  quartzose  varie- 
ties the  rocks  are  practically  quartzites,  and  their  appearance  on  fresh  frac- 
tures is  not  very  different  from  that  of  normal  quartzite.  The  intermediate 
phases  between  these  two  extremes  exhibit  naturally  intermediate  charac- 
ters. On  weathered  surfaces  the  more  dolomitic  phases  are  rough  and 
sandy,  and  of  a  light-  or  a  dark-brown  color.  The  dolomite  has  been  partly 
dissolved  and  in  the  cavities  thus  produced  quartz  has  crystallized.  A 
porous,  drusy  rock  results,  which  is  very  friable.  It  resembles  closely 
many  calcareous  sandstones.  The  replacement  of  the  d()lomite  by  the 
silica  is  not  always  confined  to  the  exposed  surface,  but  in  some  instances 
weathering  has  proceeded  to  so  great  a  depth  within  the  rock  mass  that 
no  specimens  can  be  obtained  which  do  not  possess  the  drusy  character. 

A  few  of  the  quartzose  beds  associated  with  the  dolomites  are  nearly 
pure  quartzites  that  differ  in  no  essential  respect  from  the  quartzites  of  the 
Sturgeon  formation.  They  are  fairly  fine-grained  rocks  with  a  gray  or 
purplish  color.  They  occur  in  thin  beds  rarely  more  than  2  or  3  inches 
thick,  and  are  found  at  any  horizon,  but  more  commonly  near  the  base  of 
the  dolomitic  series. 

Under  the  microscope  the  ^Durer  dolomites  are  seen  to  be  crystalline 
aggregates  of  dolomite  exhibiting  all  the  characteristics  of  this  mineral. 
The  larger  grains  are  synthetically  twinned,  but  the  smaller  ones  as  a  rule 
are  untwinned.  The  cause  of  the  various  shades  of  color  observed  in 
the  hand  specimens  is  not  recognizable  in  the  thin  section,  for  usually, 
with  the  exception  of  a  few  grains  of  ocher  and  of  hematite,  no  coloring 
matter  of  any  kind  is  noticeable  in  them.  It  seems  necessary,  therefore,  to 
regard  the  color  as  residing  in  the  carbonates  themselves,  and  not  in  any 


212  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

impurities  present  as  cementing  material  between  the  individual  grains, 
though  of  course  it  may  be  due  to  a  very  small  quantity  of  some  clay-like 
intei'stitial  substance.  The  slides  are  crossed  occasionally  by  tiny  veins  of 
calcite  and  sometimes  by  small  quartz  veins.  Little  nests  of  these  minerals 
are  also  scattered  here  and  there  through  the  mass  of  the  rock. 

The  lighter  colored  of  the  quartzose  dolomites  are  very  similar  to  the 
purer  phases  of  the  rock  except  that  they  contain  considerable  quantities  of 
quartz  in  grains  and  little  nests,  small  fragments  of  plagioclase,  and  occasion- 
ally a  few  plates  of  a  light-green  chlorite  that  has  evidently  been  derived 
from  some  mica.  The  quartz  grains  are  usually  subangular,  in  a  few  sec- 
tions thej'  are  sharp  edged,  and  in  many  they  are  beautifully  rounded  sand 
grains.  In  a  few  instances  they  are  distinctly  enlarged  These  fragmental 
grains  are  embedded  in  a  matrix  sometimes  consisting  almost  exclusively  of 
the  carbonate.  In  a  large  number  of  instances,  howevei-,  dolomite,  calcite, 
and  quartz  in  grains  of  equal  size  are  present  in  approximately  equal  quan- 
tities, composing  an  aggregate  which  under  low  powers  of  the  mici'oscope 
appears  to  be  thoroughl}'  crystalline.  Under  high  powers  the  quartz  grains 
are  seen  to  be  fragmental  and  the  carbonates  to  be  crystallized  about  them. 
Evidently  these  rocks  are  mixed  dolomitic  and  clastic  sediments  that  have 
been  partly  silicified  since  their  deposition.  They  mark  the  transition 
between  the  purer  dolomites  and  the  rocks  that  have  been  called  dolomitic 
sandstones.  These  present  no  unusual  features.  They  consist  largely  of 
fragmental  quartz  grains  embedded  in  a  crystallized  calcitic  and  dolomitic 
matrix.  Often  the  carbonates  are  in  such  small  quantity  that  the  rocks  are 
essentially  quartzites,  with  features  closely  resembling  those  of  the  Sturgeon 
quartzite. 

In  the  light-colored  phases  of  the  dolomitic  sandstones  there  are  no  con- 
stituents other  than  those  mentioned  above,  but  in  the  darker-colored  phases 
the  proportion  of  colored  components  present  is  quite  large.  These  com- 
prise ochers,  magnetite,  hematite,  rutile,  an  abundance  of  small  flakes  of 
brownish-green  chlorite  and  spicules  of  light-green  sericite  or  kaolin,  a 
few  prisms  of  tourmaline  and  grains  of  epidote.  In  other  words,  these 
rocks  appear  to  be  mixtures  of  muds,  sands,  and  calcareous  deposits  that 
were  interstratified  with  the  purer  dolomites  as  a  consequence  of  some 
local  changes  in  the  conditions  under  which  deposition  took  place.  With  a 
decrease  in  the  amount  of  dolomite  present  these  rocks,  like  the  lighter- 


ALGONKIAN,  RANDVILLE  DOLOMITE.  213 

colored  varieties,  pass  over  into  quartzites,  which  differ  from  the  Sturgeon 
quartzites  in  the  j^reseuce  of  a  large  quantity  of  crystalHzed  quartz  and 
chlorite.  The  quartz  is  in  large  grains  that  are  apparently  fragmental  and 
in  small  grains  that  appear  to  have  crystallized  in  situ.  The  latter  form 
a  matrix  by  which  the  larger  grains  and  the  chlorite  are  surrounded. 
Through  this  matrix  are  also  scattered  many  small  spicules  of  colorless 
or  light-green  sericite,  or  some  other  micaceous  mineral.  Under  low 
powers  of  the  microscope  the  chlorite  appears  to  be  fairly  homogeneous, 
but  under  high  powers  it  is  discovered  to  be  filled  with  tiny  quartz  grains 
and  with  wisps  of  a  colorless  mica.  These  are  bound  together  by  radial 
and  divergent  groups  of  chlorite,  the  whole  forming  the  flakes  noticed  under 
low  powers.  Between  the  fibers  of  the  chloi-ite  and  occasionally  embedded 
in  them  are  rutile,  magnetite,  and  ocher  grains.  The  character  of  this 
chlorite  and  its  associated  minerals  indicate  that  they  are  tlie  decomi^osition 
products  of  a  biotite.  The  quartzites  thus  appear  to  be  made  up  largely  of 
quartz  sand  and  a  fine  mud  that  has  undergone  considerable  alteration.  If 
dolomite  was  ever  present  in  them  it  has  been  removed  by  silicification 
processes. 

All  specimens  of  the  dolomites,  even  the  least  quartzose  ones,  are 
crossed  by  little  veins  of  quartz  which,  under  the  microscope,  are  discovered 
to  consist  of  crystallized  quartz  of  the  same  character  as  the  material  of  the 
cherty  quartz  rocks  to  be  described  hereafter.  The  laminae  are  usually 
not  thicker  than  a  millimeter,  but  near  the  top  of  the  formation  they  some- 
times reach  a  width  of  2  or  more  inches. 

Now  and  then  sections  of  the  dolomite  exhibit  a  schistose  structure,  in 
that  the  grains  are  all  elongated  in  a  common  direction.  There  is  no 
crushing  or  peripheral  granulation  observable;  hence  the  elongation  must  be 
due  to  the  crystallization  of  these  minerals  under  the  influence  of  pressure. 
Adams  and  Nicolson"  have  recently  shown  that  the  cataclastic  structure  in 
limestone  is  not  common.  On  the  other  hand,  they  have  shown  that  the 
sti'ucture  of  schistose  marbles  is  due  to  the  flattening  of  their  constituent 
grains  by  twinning  and  gliding.  They  have  further  proved  by  experiment 
that  the  flattening  of  the  grains  may  be  produced  by  differential  pressures 
at  temperatures  of  300°  to  400°.     At  this  temperature,  under  pressure, 

"Adams,  F   D.,  and  Nicolson,  J.  T.,  An  experimental  investigation  into  the  flow  of  marble 
Philos  Trans.  Royal  Soc.  Loudon,  Series  A,  vol.  95,  1901,  p.  363-iOl. 


214  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

marbles  are  deformed  by  flowage,  and  in  this  way  schistosity  is  superin- 
duced. The  dolomites  of  the  Randville  series  are  closely  folded;  hence 
they  were  in  the  zone  of  flowage  for  these  rocks,  and  were  subjected  to 
great  pressure  at  depths  that  must  have  had  a  much  higher  temperature 
than  that  at  the  surface.  The  structure  of  the  schistose  phase  is  that  which 
should  be  expected  under  the  conditions,  and  is  confirmatory  of  the  implied 
Anew  of  Adams  and  Nicolson  that  limestones  in  folded  regions  should 
exhibit  schistosity,  due  to  flattening  of  their  components  as  the  result  of 
flowage.  That  the  schistosity  of  the  Randville  dolomites  is  not  more 
marked  than  it  is  maj-  be  due  to  the  fact  that  they  were  raised  from  the 
zone  of  flowage  to  the  zone  of  fracture  at  the  end  of  Lower  Huronian  time, 
and  since  then  have,  in  large  measure,  been  recrystallized  by  percolating 
waters. 

The  quartzose  dolomites  are  more  apt  to  exhibit  schistosity  than  the 
purer  varities.  Indeed,  nearly  all  the  dolomitic  rocks  that  appear  schistose 
in  the  hand  specimen  contain  more  or  less  quartz.  In  the  nonquartzose 
dolomites  the  schistosity  is  due  to  flattening  of  the  dolomite  grains.  There 
is  no  granulation  of  the  components.  In  the  quartzose  dolomites,  on  the 
other  hand,  graiuilation  is  observed  on  a  comparatively  large  scale.  The 
larger  of  their  quartzose  components  have  been  crushed  into  quartz  mosaics, 
which  may  be  lenticular  in  shape  or  which  may  possess  the  general  outUnes 
of  the  original  grains  from  which  they  were  formed.  From  the  ends  of  the 
leuticules  long  tails  of  a  very  fine-grained  mosaic  often  extend  into  the 
surrounding  dolomite,  and  here  and  there  scattered  tlu-ough  the  matrix  are 
little  n-regular  masses  of  the  same  mosaic  that  may  be  detached  portions  of 
shattered  grains.  Quartz  nests  are  also  found  in  these  rocks.  These  difi"er 
from  the  mosaics  in  their  very  irregular  outline  and  in  the  very  much 
coarser  grain  of  the  mineral  composing  them.  The  dolomite  matrix  shows 
Httle  evidence  of  crushing.  It  is  an  extremely  fine-grained  crystalline 
aggregate,  containing  here  and  there  an  embedded  quartz  grain,  and  some- 
times a  few  flakes  of  chlorite,  sericite,  or  other  secondary  mineral.  The 
schistosity  of  these  rocks  is  due  almost  exclusively  to  the  flattening  of  the 
quartz  grains. 

Not  all  the  dolomites  were  deformed  by  plastic  flowage,  however,  for 
many  specimens  which  in  the  ledge  and  in  the  hand  specimen  appear  to 
be  massive,  when  examined  in  thin  section  are  found  to  be  minutely  brec- 


ALGONKIAN,  RANDVILLE  DOLOMITE.  215 

ciated.     They    consist  of  dolomite    fragments    embedded  in  a  matrix  of 

dolomite,  calcite,  and  qnartz.     Some  of  the  latter  mineral  is  plainly  frag- 

mental,  but  much  of  it  was  deposited  as  little  nests  of  small  grains  between 

larg-e  crystalloids  of  calcite  and  smaller  ones  of  dolomite. 

Only  one  analysis  of  the  dolomites  has  been  made,  so  far  as  known,  but 

it  probably  represents  very  accurately  the  composition  of  the  purer  kinds. 

The  specimen  analyzed  was  a  pink  variety  from  shaft  B  of  the  Chapin 

mine.     It  was  made  by  Mr.  E.  E.  Brewster,  now  chemist  of  the  Pewabic 

mine,  who  kindly  furnished  the  results  for  publication.     The  constituents 

as  determined  and  the  components  in  the  dolomite  corresponding  to  them 

are  as  follows: 

Analysis  of  dolomite  from  Chapin  mine. 

CaO 30.97=CaCO3 55.20 

MgO 20.48=MgCO3 42.84 

Fe 80=FeCO3 1.66 

P2O5 -- 05=Apatite 11 

ALA ----        .20=A1A 20 

Residue .  73=Residue  (mostly  silica) .73 


Total 100.  74 

The  rock  is  thus  an  almost  normal  dolomite  of  the  composition  CaCOg  + 
MgC03. 

DOLOMITE    BRECCIAS   AND    CONGLOMERATES. 

The  presence  of  anastomosing  quartz  veins  in  the  massive  dolomites, 
the  existence  of  schistosity  in  many  specimens,  and  the  minutely  brecciated 
structure  observed  in  the  thin  sections  of  specimens  from  apparently 
homogenous  beds,  indicate  that  the  dolomite  series  has  been  deformed 
under  pressure.  In  most  instances  this  pressure  did  not  express  itself  in 
crushing  sufficientl}'  marked  to  be  detected  in  the  ledge.  But  in  some 
places,  more  particularly  at  the  apices  of  folds  and  along  contacts  with 
overlying  formations  where  accommodations  to  stresses  resulted  in 
sudden  movements,  the  crushing  was  so  severe  that  the  rock  was  actually 
fractured  on  a  large  scale,  and  breccias  produced.  These  consist  of 
sharp-edged  and  lenticular  fragments  of  dolomite  separated  from  one 
another  by  seams  and  interstitial  masses  of  dolomitic  material  with  which 
a  small  quantity  of  quartz  sand  is  admixed.  In  some  beds  the  fragments 
make  up  the  greater  portion  of  the  rock  mass,  as  is  the  case  in  the  cliff  at 
the   northeast   end   of  the  little   valle}"  east  of  the   Aragon   mine  (see   PI. 


216  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

XVI,  A).  In  other  beds  the  interstitial  substance  is  in  greater  quantity 
and  the  fragments  sparse.  In  the  former  case  the  autoclastic  character  of 
the  breccia  is  unquestionable.  In  the  latter  case  the  rock  looks  very  much 
like  a  breccia  of  fragments  cemented  together  by  foreign  material.  This 
is  true  of  some  of  the  breccia  at  Iron  Hill. 

Under  the  microscope  the  dolomitic  breccias  are  seen  to  differ  but 
little  from  the  finely  crushed  dolomites  referred  to  above  (p.  214),  except 
in  the  greater  size  of  the  fragments.  These,  as  has  already  been  described, 
are  mainly  angular  pieces  of  dolomite  and  of  the  rocks  associated  with  the 
dolomites.  In  some  instances  the  matrix  surrounding  the  larger  dolomite 
fragments  is  made  up  of  small  angular  fragments  of  the  same  rock  cemented 
by  an  aggregate  of  large,  colorless  crystalloids  of  calcite.  The  small  and 
the  large  fragments  of  the  original  rock  are  surrounded  by  little  zones  of 
ocher  that  seem  to  have  been  deposited  upon  them  before  the  crystalli- 
zation of  the  calcite  cement.  The  rocks  are  undoubted  autoclastic  breccias 
produced  from  the  purer  dolomite  beds. 

In  most  cases  the  original  rock  was  a  quartzose  dolomite,  and  the 
resulting  breccia  consequently  contains,  in  addition  to  dolomite  and  calcite, 
more  or  less  fragmental  quartz,  the  quantity  present  depending  upon  the 
quantity  in  the  original  rock.  Some  of  the  fragmental  quartzes  show 
enlargements,  with  the  added  material  often  extending  for  considerable 
distances  from  the  fragmental  nuclei  into  the  surrounding  carbonates. 
While  much  of  the  dolomite  in  the  matrix  may  originally  have  been  in 
clastic  grains  it  is  now  plainly  in  forms  that  have  crystallized  in  situ.  The 
calcite,  which  is  nearly  always  in  comparatively  large  grains,  is  clearly 
newly  deposited.  Much  of  the  recrystallized  carbonates  have  been  depos- 
ited as  fringes  around  the  fragments  of  dolomite,  which  are  sun-ounded  by 
zones  composed  of  many  elongated  grains  lying  side  by  side  and  forming 
a  radial  aggregate  completely  enveloping  the  fi-agmental  nuclevis. 

In  some  places,  particularly  in  the  interstices  between  tlie  larger 
fragments,  the  matrix  is  schistose,  when  the  dolomite  grains  are  flattened  in 
the  plane  of  schistosity  and  their  twinning  lamellse  are  curved.  The 
breccias  in  which  the  schistosity  is  most  marked  do  not  always  exhibit  this 
structm'e  in  the  hand  specimens.  Usually  their  embedded  fragments  can 
be  seen  on  the  weathered  surfaces  to  lie  in  the  matrix  with  their  long  axes 
in  a  uniform  direction,  but  on  the  fresh  fractures  where  the  fragments  can 
not  be  distinguished  no  trace  of  schistosity  can  be  detected. 


PLATE   XVI 


217 


PLATE    XVI. 

Fig.  a. — Brecciated  Randville  dolomite.  In  wall  at  east  end  of  little  gorge  running  east 
from  the  Aragon  mine.  Fragments  and  matrix  are  composed  of  tiie  same  kind  of  dolomite.  Frag- 
ments are  all  sharp  edged. 

Fig.  B. — Dolomite  conglomerate.  At  Iron  Hill  in  sec.  32,  T.  40  N.,  R.  29  W.  The  large 
fragments  are  rounded,  the  smaller  ones  are  angular.  Both  fragments  and  matrix  are  crossed  by 
joint  cracks  in  which  cherty  quartz  has  been  deposited.  The  quartz  seams  now  project  from  the 
weathered  surface.  The  matrix  is  more  siliceous  than  the  fragments,  partly  because  it  contains  a 
thicker  network  of  the  quartz  seams,  and  partly  because  it  contains  a  considerable  proportion  of  sand 
grains.  Consequently  surfaces  of  fragments  are  depressed.  The  fragments  are,  moreover,  often 
surrounded  by  narrow  projecting  seams  of  the  cherty  quartz.  The  bedding  of  the  dolomite  in  the 
fragments  may  often  be  plainly  seen. 

218 


U.   S.    GEOLOGICAL    SURVEY 


MONOGRAPH    XLVI       PL. 


A.      BRECCIATED    RANDVILLE   DOLOMITE   IN    WALL   AT    EAST    END   OF    LITTLE   GORGE   RUNNING    EAST   FROM   THE 

ARAGON    MINE. 


Jl.     DOLOMITE  CONGLOMERATE   AT    IRON    HILL   IN    SEC.   32,   T.  40   N.,    R,   29   W. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  219 

In  occasional  instances  beds  are  met  with  in  which  the  inchised. 
fragments  are  rounded.  The  rock  then  is  a  definite  conglomerate.  Some 
of  these  occur  locally,  forming  layers  lying  between  thick  beds  of  nearly 
massive  dolomite.  The  conglomerates  of  this  kind  are  composed  of 
dolomite  pebbles  of  one  color  in  a  dolomitic  matrix  of  anotlier  color. 
They  may  be  intraformational  in  character,  like  those  described  by  Walcott " 
in  tlie  Paleozoic  series  of  New  England,  Pennsylvania,  Virginia,  and 
elsewhere. 

Most  of  these  conglomerates  differ  from  the  nonconglomeratic  beds 
with  which  they  are  associated  only  in  the  possession  of  fragments.  The 
fragments  are  almost  exclusively  dolomite  in  the  beds  whose  matrix  is 
dolomitic.  In  those  conglomerates  in  which  the  matrix  is  strongly 
quartzose,  the  fragments  may  be  dolomite  or  slate.  They  are  identical 
in  character  with  the  material  of  neighboring  dolomite  or  slate  beds,  and 
the  matrix  is  precisely  similar  to  the  material  of  closely  associated  quai-tzose 
beds  In  no  case  is  there  anything  discoverable  in  the  thin  section  that 
contradicts  the  view  that  these  conglomerates  are  intraformational  beds. 
Their  material  is  all  from  nearby  sources.  There  is  intermixed  with  this  no 
foreign  material. 

A  few  other  conglomerates  are  very  closely  allied  to  the  breccias,  from 
which  they  difter  only  in  the  shapes  of  their  fragments.  These  are  rounded 
or  subangular,  and  are  composed  exclusively  of  dolomitic  material  and 
quartz — the  former  predominating.  When  the  matrix  contains  but  little 
quartz  the  fragments  usually  consist  of  the  purer  varieties  of  dolomite; 
when  quai-tz  is  abundant  in  the  matrix  the  fragments  are  quartzose  dolomite. 
These  rocks  are  clearly  autoclastic,  their  fragments  having  been  rounded 
by  attrition. 

There  is,  however,  another  small  group  of  conglomerates  represented 
almost  exclusively  by  the  conglomerate  of  Iron  Hill,  the  origin  of  which 
is  completely  problematical.  In  the  Iron  Hill  rock  the  j^ebbles  are 
nearly  all  of  dolomite.  The  few  remaining  ones  are  mainly  chert,  and  a 
very  few  are  quartz  or  quartzite.  They  vary  in  size  from  those  of  minute 
dimensions  to  others  more  than  a  foot  in  diameter.  PI.  XVI,  i?  is  a 
reproduction  of   a    photograph  of  a  portion  of  this  conglomerate.     The 

"The  Cambrian  rocks  of  Pennsylvania:  Bull.  U.  S.  Geol.  Survey  No.  134,  1896,  p.  34-46. 


220  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

sparse  matrix  between  the  pebbles  is  finely  ground  up  dolomite  and  chert 
and  small  grains  of  sand.  The  appearance  of  the  rock  suggests  strongly 
that  it  is  a  true  conglomerate  formed  from  the  debris  of  the  underlying 
dolomite  and  cherty  quartzite  beds,  but  its  relations  with  these  beds  and 
with  typical  breccias  are  so  complicated  that  no  certain  conclusion  to  this 
eff'ect  has  been  arrived  at  (see  pp.  257-260).  If  a  true  conglomerate,  it 
naturally  belongs  at  the  base  of  the  formation  overlying  the  dolomite,  and 
is  probably  Upper  Huronian.  It  is  referred  to  in  this  place  because  of  its 
lithological  similarity  to  the  other  members  of  the  Randville  series 

Another  conglomerate  that  ma}^  belong  with  this  group  occurs  near 
the  center  of  sec.  35,  T.  40  N.,  R.  30  W.,  on  the  branch  railroad  running 
through  this  section.  It  appears  to  be  a  true  conglomerate,  although  it  is 
of  a  different  character  from  that  at  Iron  Hill.  Its  matrix  is  a  coarse 
dolomitic  or  calcareous  sandstone,  and  its  pebbles  are  largely  of  slate  and 
other  argillaceous  rocks  associated  with  the  dolomites.  The  rock  may, 
however,  be  an  intraformational  conglomerate,  like  the  majority  of  the 
conglomerates  in  the  series. 

In  the  conglomerate  at  Iron  Hill  the  fragments  are  rounded  and  very 
pebble-like.  Most  of  them  consist  of  dolomite  or  quartz,  but  some  are 
composed  of  chert  or  quartzite.  Most  of  the  fragments  are  suiTOunded  by 
narrow  black  borders  made  np  of  numerous  scales,  grains,  and  small 
crystals  of  an  opaque  substance,  intermingled  with  indefinitely  outlined 
masses  of  green  chloritic  material.  The  same  opaque  substance  surrounds 
the  larger  quartz  grains  in  the  matrix  and  is  scattered  irregularly  through 
some  of  the  components  of  the  groundmass.  Just  within  the  borders  the 
rims  of  the  dolomite  fragments  sometimes  show  an  irregular  zone  of  quartz, 
as  if  the  dolomite  has  been  corroded  by  siliceous  solutions  and  a  portion  of 
the  carbonate  had  been  replaced  by  silica. 

The  matrix  of  the  rock  is  like  that  of  the  ordinary  breccias.  There 
are  a  few  more  fragmental  grains  of  quartz  in  it,  but  otherwise  the  two  are 
similar.  At  first  glance  this  conglomerate  would  be  pronounced  sedi- 
mentary in  origin,  because  of  the  great  number  of  clastic  quartz  grains  in 
it,  but  when  it  is  recalled  that  much  of  the  nonconglomeratic  dolomite  is 
quartzose  and  that  the  quartz  is  present  in  them  as  distinctly  clastic  sand 
grains,  the  evidence  from  this  component  is  valueless.  Nevertheless,  the 
general  appearance  of  some  of  the  rocks  is  strongly  suggestive  of  a  sedi- 


ALGONKIAN,  RANDVILLE  DOLOMITE.  221 

mentaiy  origin.     The  presence  of  the  quartzite  and  chert  pebbles  lends 
some  sujDport  to  this  view. 

TALCOSE   SCHISTS. 

At  some  places  the  dolomites,  at  their  contacts  with  the  overlying  iron 
formation,  have  been  entirely  changed  from  their  original  condition  and 
are  now  represented  by  a  very  different  rock,  com])osed  largely  of  talc  and 
serpentine.  This  talcose  rock  seems  to  be  limited  in  its  occurrence  to  those 
places  where  shearing  must  have  been  at  a  maximum.  It  is  found  in  large 
quantities  facing  the  dolomite  underlying  the  iron  formation  in  the  close 
folds  of  the  Norway  and  Aragon  mines,  in  less  quantities  in  the  same 
position  in  the  Walpole  and  Pewabic  folds,  and  often  as  a  thin  layer 
between  the  dolomite  and  the  basal  members  of  the  iron  formation  in  those 
portions  of  the  district  where  subordinate  folding  has  not  taken  place.  It 
occurs,  also,  as  pebbles  in  the  ore  and  dolomite  conglomerate  overlying  the 
bedded  dolomite  in  the  Norway  mine  and  to  some  extent  in  the  matrix  of 
this  conglomerate. 

The  rock  is  soft  and  unctuous.  It  is  usually  of  a  dark  reddish-purple 
color,  mottled  with  white  patches  and  cut  into  prismatic  and  lenticular 
masses  by  three  systems  of  veins,  intersecting  one  another  by  very  acute 
and  very  obtuse  angles.  The  rock  is  thus  broken  up  into  a  large  number 
of  separate  portions  with  long  rhomboidal  cross  sections,  all  lying  in  an 
approximately  parallel  direction.  It  therefore  possesses  as  a  whole  a 
roughly  schistose  structure.  The  material  between  the  veins  is  generally 
massive,  only  incipient  schistosity  being  noted  in  a  few  places.  Along  the 
walls  of  the  veins,  however,  differential  movement  has  taken  place  and 
slickensides  have  been  ^jroduced.  The  material  covering  the  slickensided 
surfaces,  that  causing  the  white  mottling  within  the  rock  mass,  and  the 
filling'  of  the  veins,  is  all  white  talc.  In  the  Norway  conglomerate  the  talc 
rock  differs  from  that  just  described  in  that  it  contains  a  large  quantity  of 
dolomite,  intermingled  with  the  talc  as  small  fragments,  small  crystals,  and 
as  druses  along  little  cracks.  In  the  Pewabic  mine  the  rock  is  lighter  in 
color  than  commonly,  and  contains  fragmeutal  quartz  and  other  clastic 
material,  probably  derived  from  the  upper  wall  of  the  shearing  zone. 

In  thin  sections  the  talcose  schists  do  not  present  any  very  definite 
characteristics.  A  great  number  of  small  rounded  grains  and  many  crys- 
tals of  hematite  lie  in  an  almost  colorless  groundmass,  which,  under  crossed 


222 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


nicols,  is  seen  to  be  made  up  of  small  angular  grains  of  quartz  and  flakes 
and  shreds  of  micaceous  minerals  lying  in  a  mass  of  structureless  material 
which  apparently  has  almost  no  influence  on  polarized  light.  The  mica- 
ceous minerals  are  light  green  in  ordinary  light  and  have  a  small  refractive 
index.  Some  of  Ihe  fibers  polarize  in  j^ellow  and  reddish  tints,  and  others 
in  the  blues  and  grays  of  the  first  order.  These  are  taken  to  be  talc  or 
kaolin  and  serpentine.  The  ill-defined  mesostasis  may  be  serpentine. 
Some  of  the  quartz  grains  have  very  definite  outlines  that  separate  them 
sharply  from  the  remainder  of  the  rock,  but  the  same  mineral  is  present 
also  in  indefinite  areas  that  grade  off  into  the  surrounding  weakly  polarizing 
material.  In  these  areas  the  quartz  can  be  detected  only  by  the  aid  of  a 
mica  plate.  The  distinct  grains  appear  to  have  a  difierent  origin  from  the 
indistinct  masses,  which  were  probably  deposited  contemporaneousl}"  with 
the  serpentin'fe,  talc,  and  kaolin.  Many  little  veins  traverse  the  sections, 
and  in  these  there  is  a  predominance  of  the  brightly  polarizing  talc  fibers 
stained  in  spots  by  brown  limonite. 

A  specimen  of  the  rock  from  the  Aragon  mine  was  analyzed  by  Mr. 
George  Steiger,  of  the  U.  S.  Geological  Survey  laboratory.  The  result  of 
this  analysis  appears  below  in  column  I: 

Comjposition  of  talcose  schist  from  the  Aragon  mine. 


I. 

Talc. 

Serpentine. 

Kaolin. 

Hematite. 

Quartz. 

Total. 

SiO 

49.56 

.60 

10.12 

5.87 

.13 

Trace. 

None. 

.72 

20.53 

None. 

None. 

4.  .50 

7.66 

.04 

None. 

19.63 

11.13 

11.10 

7.70 

49.56 

TiO 

Al  0. 

..34 
.12 

.31 
.36 

9.47 



10.12 

Fe  Oo 

5.10 

5.58 

FeO 

MnO 

Trace. 

Trace. 

BaO 

CaO 

1 

MsO 

10.  .31 

10.32 

20.63 

K  0 

NaO 

1 

H^O     110° 

H„O4-110° 

1.39 

3.64 

3.  .32 

8.35 

PO- 

COi 

Total.. 

99.73 

31.79 

25.76 

23.89 

5.10 

7.70 

94.24 

ALGONKIAiSl,  RANDVILLE  DOLOMITE.  223 

Excluding  the  Fe203,  which  is  sufficiently  accounted  for  by  the  large 
quantit}'  of  hematite  in  the  rock,  the  essential  features  of  the  analysis  are 
the  presence  of  MgO  and  AljOg  to  the  practical  exclusion  of  all  other 
constituents  except  silica  and  water.  The  data  at  hand  are  not  full  enougli 
to  enable  one  to  calculate  with  certainty  the  niineralogical  composition  of 
the  I'ock.  It  is  certain,  however,  that  its  components  are  few  in  number 
and  that  they  are  limited  to  magnesian  and  aluminous  compounds  If  we 
assume  that  the  MgO  is  all  present  in  talc  and  serpentine  in  equal  amounts 
and  that  the  AI2O3  is  limited  to  kaolin,  and  make  the  further  assumption 
that  the  magnesian  minerals  have  the  same  composition  as  the  correspond- 
ing substances  deposited  in  the  ores  (see  p.  390),  it  is  a  comparatively  simple 
matter  to  account  for  all  the  constituents  enumerated  in  the  analysis.  A 
calculation  based  on  the  above  assumption  shows  the  rock  to  be  composed 
of  31.79  per  cent  talc,  25.76  per  cent  serpentine,  "23.89  per  cent  kaolin, 
7.70  per  cent  quartz,  5  10  per  cent  hematite,  0.60  per  cent  rutile  (if  the 
Ti02  is  present  as  rutile  needles),  0.42  per  cent  magnetite,  and  0.17  per 
cent  apatite.  There  remains  over  unaccounted  for  only  0.59  per  cent  CaO, 
whicli  may  well  be  present  in  any  one  of  the  three  principal  constituents. 
The  amount  of  water  required  to  satisfy  the  demands  of  this  calculation  is 
0.69  per  cent  in  excess  of  the  amount  reported  in  the  analysis  of  the  rock. 
The  calculation,  however,  is  based  on  the  assumption  that  the  serpentine 
contains  14.08  per  cent  water  (see  analysis,  p.  390)  which  is  a  larger  quantity 
by  over  1  per  cent  than  the  formula  of  this  mineral  requires.  Since  the 
determination  of  this  constituent  was  by  loss  it  is  probable  that  it  includes 
some  water  driven  off  at  a  low  temperature. 

The  proportion  of  the  various  components  demanded  to  satisfy  the 
principal  mineral  constituents  are  given  in  the  columns  above  under  appro- 
priate headings.  To  the  sum  under  the  column  headed  "Total"  there  should 
be  added  6.28,  which  represents  the  hygroscopic  water,  the  quantities  of 
magnetite,  rutile,  and  apatite  calculated  as  present  in  the  rock,  and  the 
excess  of  CaO  indicated  by  the  analysis,  and  there  should  be  deducted 
froni  this  sum  0.69,  representing  tlie  calculated  excess  of  combined  water 
present  in  the  serpentine,  talc,  and  kaolin  above  that  found  by  the  analysis. 
The  result  of  these  processes  will  correspond  with  the  sum  of  the  constit- 
uents determined  as  being  present  in  the  sample  analyzed. 


224  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  composition  of  the  schist  as  giveu  above  corresponds  very  well 
with  the  conclusions  derived  from  a  study  of  its  thin  sections  so  far  as  the 
nature  of  its  constituents  is  concerned.  In  most  sections,  howevei',  the 
talc  appears  to  be  in  less  amount  than  the  above  calculation  would  indicate, 
and  the  serpentine  (if  the  feebly  polarizing  matrix  is  composed  of  this 
mineral)  in  greater  amount.  However,  variations  in  the  quantities  of 
these  two  minerals  assumed  to  be  present  would  effect  only  the  proportion 
of  free  silica  in  the  calculation,  an  increase  in  the  quantity  of  serpentine 
causing'  a  con-esponding  increase  in  the  calculated  proportion  of  the  free 
quartz.  The  essential  features  of  the  chemical  and  optical  study  are  the 
same.  The  rock  is  composed  mainly  of  talc,  serpentine,  kaohn,  quartz, 
and  hematite.  Whether  it  was  derived  directly  from  dolomite  or  whether 
it  was  originall}^  a  fragmental  rock  composed  largely  of  dolomitic  debris 
can  not  now  be  told,  as  all  of  its  original  components,  except  possibly  a 
few  quartz  grains,  have  been  replaced  by  secondary  minerals  that  were  in 
all  probability  deposited  from  the  same  kinds  of  solutions  that  elsewhere 
in  the  ore  bodies  deposited  talc,  serpentine,  and  quartz.  The  presence  of 
kaolin  in  the  schist  may  be  looked  upon  as  evidence  that  the  original  rock 
was  a  sediment,  but  tliis  is  only  a  surmise,  as  the  waters  that  deposited  the 
talc  and  serpentine  may  have  brought  with  them  aluminous  salts. 

If  the  rock  were  originally  a  portion  of  the  dolomite  its  alteration  into 
talc  necessitated  the  removal  of  the  calcium  carbonate  and  the  replacement 
of  the  carbon  dioxide  of  the  magnesium  carbonate  by  silica.  The  dissolved 
calcium  carbonate  was  carried  off  and  some  of  it  was  deposited  as  calcite 
in  the  ores  and  along  watercourses  (see  p.  387).  Some  of  the  magnesium 
carbonate  was  also  carried  off  in  solution.  It  now  appears  as  dolomite  in 
the  ores  and  another  poi'tion,  changed  to  silicates,  occurs  as  deposits  of 
serpentine  and  talc  (see  pp.  389-390).  The  remaining  magnesian  silicates, 
together  with  the  impurities  originally  existing  in  the  dolomite  and  others 
contributed  by  the  water,  constitute  the  impure  talcose  rock.  The 
conditions  favoring  its  production  appear  to  be  movement  in  a  shearing 
zone  attended  by  chemical  action  brought  about  by  percolating  water. 
These  conditions  are  most  perfectly  provided  for  in  the  pitching  subordinate 
folds  occupied  by  the  ore  deposits  and  in  the  steeply  dip^jing  surfaces  of 
contact  planes  between  two  formations.  To  a  minor  degree  the  conditions 
also  prevail  along  fault  planes,  and  it  is  noticeable  that  along  sUckensided 
surfaces  of  such  fault  planes  in  the  dolomite  talc  is  also  found. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  225 

Because  of  its  impervious  character,  troughs  hned  with  the  talc-schist 
afford  especially  favorable  situations  for  the  deposition  of  ore  bodies. 

ARGILLACEOUS    ROCKS. 

The  arg-illaceous  members  of  the  dolomite  series  are  not  abundant. 
They  consist  of  a  few  rocks  interbedded  with  the  dolomites  and  dolomitic 
quartzites  at  various  horizons  in  layers  varying  from  the  fraction  of  an  inch 
to  several  feet  in  thickness.  Together  with  thin  beds  of  quartzite,  they  also 
constitute  definite  congeries  of  beds  that  appear  to  be  somewhere  near  the 
top  of  the  series.  Sometimes  the  slaty  beds  in  these  groups  are  as  much 
as  40  feet  in  thickness,  but  usually  the  aggregate  is  made  up  of  alternations 
of  quartzites  and  slaty  rocks  in  layers  not  more  than  5  or  10  feet  thick. 
The  slaty  rocks  are  best  exposed  along  the  railroad  running  through  sec. 
35,  T.  40  N.,  R.  30  W.,  and  in  the  ledges  south  of  the  center  of  sec.  12,  T. 
39  N.,  R.  29  W. 

Most  of  the  slates  are  soft,  light-gray  or  dark-gray,  schistose  rocks, 
some  of  which  resemble  very  closely  some  phases  of  sericite-schists.  Others 
are  typical  black  slates,  still  plainly  marked  by  bedding  lines.  These  are 
rare  and,  so  far  as  known,  are  confined  to  the  set  of  interbedded  slates  and 
quartzites  referred  to  above  as  constituting  a  definite  portion  of  the  dolomite 
series  near  its  top.  All  the  argillaceous  rocks  except  the  black  slates  con- 
tain considerable  dolomitic  material. 

In  addition  to  these  slates,  thin  seams  of  an  argillaceous  dolomite,  with 
a  schistose  structure  and  a  purplish-pink  color,  often  occur  between  massive 
beds  of  dolomite.  In  many  instances  they  appear  to  be  merely  the  sel- 
vages of  softer  layers  of  the  dolomite  rendered  schistose  by  the  movements 
of  accommodation  between  stronger  beds.  Others  may  actually  represent 
thin  beds  of  argillaceous  material  deposited  between  beds  of  purer  dolomite. 

A  third  group  of  argillaceous  rocks  should  be  referred  to  here,  though 
the  slates  may  belong  at  the  base  of  the  overlying  formation.  These  are 
red,  white,  light-purple,  or  light-gray,  fine-grained,  often  fissile,  calcareous 
shales,  with  a  dull  luster  on  fresli  fracture  surfaces.  The  rocks  are  known 
only  from  test  pits  and  drill  holes.  They  usually  occupy  an  extremely 
narrow  belt  between  well-defined  dolomite  and  well-characterized  members 
of  the  overlying  iron  formation.  Their  relations  with  the  contiguous  rocks 
have  not  been  seen ;  consequently  their  exact  position  has  not  been  definitely 
determined.  In  the  coarser  varieties  quartz  grains  are  easily  distinguish- 
MON  XLVI — 04 1.5 


226  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

able.  These  rocks  may  be  built  up  of  the  detritus  of  the  dolomite  series 
and  consequently  may  be  the  basal  layers  of  the  Upper  Huroniau  beds. 
On  the  other  hand,  they  may  be  integral  portions  of  the  Randville  series  at 
some  distance  from  its  top  that  have  in  some  places  been  made  to  appear  at 
the  top  of  the  series  by  the  removal  of  overlying  beds  during  the  inter- 
Huronian  erosion  jieriod.  In  any  event,  wherever  they  are  found  they 
always  mark  the  near  proximity  of  the  contact  between  the  dolomite  series 
and  the  overlying  Vulcan  formation. 

None  of  these  slates  present  any  features  of  peculiar  interest  from  a 
microscopical  jjoint  of  view.  The  black  and  the  gray  slates  are  like  the 
siliceous  slates  of  the  Hanbury  formation,  to  be  discussed  later  (see  pp.  463- 
464),  and  the  sericite  phases  are  like  corresponding  phases  in  the  Hanbury 
series. 

The  white  and  light-purple  slates  between  the  dolomite  and  the  Vulcan 
formation  are  composed  of  small  quartz  grains,  small  flakes  of  chlorite,  a 
few  larger  ones  of  muscovite,  granules  and  irregular  masses  of  ocher,  and 
innumerable'  tiny  plates  of  a  light-green  or  colorless  mineral  that  resembles 
kaolin.  This  kaolinitic  substance  is  included  in  all  the  other  constituents, 
and  forms,  together  with  some  secondary  quartz,  an  aggregate  by  which  the 
other  comj^onents  are  surrounded.  Some  dolomite  and  calcite  are  also 
present  in  little  nests,  but  not  in  any  considerable  quantity.  A  few  rutile 
needles,  irregular  grains  of  zircon,  and  an  occasional  group  of  small  epidote 
grains  are  also  universally  present.  The  color  of  the  pink  slates  is  due 
to  a  great  number  of  very  small  round  granules  and  tiny  dust-like  particles 
of  hematite  and  limonite  that  are  scattered  indiscriminately  through  all  the 
other  constituents. 

The  characteristic  features  of  these  slates  which  distinguish  them  from 
the  younger  slates  in  the  district  are  the  abundance  of  kaolin  in  them  and 
the  absence  of  any  large  quantity  of  sericite  and  chlorite. 

CHERTT  QUARTZ  ROCKS. 

The  cherty  quartz  rocks  are  found  only  at  the  top  of  the  Randville 
formation  and  never  elsewhere  in  the  series.  They  are  fine-grained, 
vitreous,  or  saccharoidal,  in  places  drusy,  massive,  siliceous  rocks  with  a 
white,  gray,  pink,  red,  or  dark-purple  color.  Because  they  are  composed 
partly  of  quartz  grains  and  partly  of  chemically  deposited  silica  they  have 
been  called  cherty  quartz  rocks.     The  red  and  purple  varieties  resemble 


ALGONKIAN,  RANDVILLE  DOLOMITE.  227 

very  closely  some  of  the  jaspilites  in  the  iron  formation.  They  all  weather 
with  a  smooth,  polished  surface  much  like  that  of  some  of  the  most  exposed 
ledges  of  the  Sturg-eon  quartzites.  They  occur  at  only  a  few  localities, 
always  overlying  normal  dolomite.  Their  l^est  developments  are  at  Iron 
Hill,  in  sec.  32,  T.  40  N.,  R.  29  W.,  and  in  the  cliff  north  of  the  Common- 
wealth pit  or  the  new  Keel  Ridge  mine,  in  sec.  32,  T.  40  N.,  R,  30  W. 
(see  pp.  261-263). 

Wherever  found  the  rock  is  crossed  by  quartz  veins  that  sometimes  run 
for  short  distances  in  parallel  directions  and  then  anastomose,  and  at  other 
times  anastomose  irregularly  over  all  exposed  surfaces,  cutting  the  rock  up 
into  parts,  ])roducing  a  breccia.  In  other  instances  the  rock  is  fractured, 
and  the  fragments  thus  produced  are  cementqd  by  a  mixture  of  fragmental 
and  chemically  deposited  silica.  The  breccias  produced  by  both  methods 
are  practically  identical.  They  consist  of  sharply  angular  fragments  of  one 
color  in  a  matrix  of  some  other  color.  Both  matrix  and  frag-ments  have 
essentially  the  same  composition  and  the  same  texture,  though  the  texture 
of  the  matrix  in  some  specimens  may  be  a  little  coarser  than  that  of  the 
inclosed  fragments.  In  some  places  it  is  also  drusy  through  the  solution 
of  some  constituent  and  the  deposition  of  quartz  in  the  walls  of  the  cavities 
thus  formed. 

The  presence  of  the  cherty  quartz  rocks  at  some  places  and  their 
absence  from  others  is  accounted  for  by  the  supposition  that  they  were 
once  continuous  over  the  dolomite,  and  that  the  erosion  that  marked  the 
interval  between  Lower  Huronian  and  Upper  Huronian  times  cut  down 
irregularly  into  the  Randville  series,  in  some  places  removing  only  the 
upper  layers  of  the  cherts  and  at  other  places  removing  the  entire  deposit. 
Their  almost  universal  brecciated  character  may  be  due  to  the  fact  that 
they  occur  along  a  contact  zone  where  movements  of  accommodation  that 
must  have  attended  the  folding  of  the  district  were  naturally  accentuated 
and  to  the  further  fact  that  because  of  their  brittle  character  the  cherty 
rocks  yielded  to  stresses  more  easily  by  fracture  than  by  shearing. 

In  natural  light,  under  low  powers  of  the  microscope,  tlie  more  massive 
phases  of  the  cherty  quartzites  aj)pear  as  very  light-yellow,  transparent, 
homogeneous  rocks  speckled  by  little  clumps  of  a  dark-yellow  substance 
which  under  high  powers  is  resolved  into  masses  of  ocher,  and  dusted  witli 
little  opaque  dots,  which  on  stronger  inagnification  are  seen  to  be  o-rains 


228  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

of  hematite.  In  polarized  light  the  sections  become  very  fine-grained 
aggregates  of  interlocking  quartz  grains,  cut  here  and  there  by  veins  of 
quartz,  and  containing  occasionally  little  areas  of  the  same  mineral  in 
which  the  grains  are  several  times  the  size  of  those  in  the  surrounding 
ao-oreo-ate.  Very  small  flakes  of  a  colorless  micaceous  mineral  are  scat- 
tered  here  and  there  through  the  aggregates.  In  one  or  two  sections 
caleite  or  dolomite  is  abundant.  It  is  in  very  small  rounded  grains 
embedded  in  the  quartz  and  in  irregular  masses  apparently  interlocking 
with  the  quartz  grains.  Occasionally  there  is  a  grain  of  quartz  present  in 
the  slide  which  looks  as  though  it  might  be  fragmental,  but  usually  no 
traces  of  clastic  characters  can  be  detected  in  any  of  the  components. 
Here  and  there  in  the  midst  of  the  fine-grained  aggregate  round  and 
irregularly  shaped  areas  of  quartz  mosaics  are  met  with  that  may  perhaps 
mark  the  positions  of  large  grains  in  an  original  sediment.  The  structure 
of  the  mosaic  is  always  much  coarser  than  that  of  the  main  portion  of  the 
rock  mass,  and  often  many  of  its  constituent  grains  are  crossed  by  strain 
shadows. 

Like  the  cherts  in  the  Gogebic  district,  those  in  the  Menominee  dis- 
trict are  markedly  breceiated.  Reference  has  already  been  made  to  the 
abundance  of  breceiated  forms  in  the  descriptions  of  the  macroscopic  fea- 
tures of  the  rocks.  When  examined  in  thin  section  it  is  soon  noted  that 
many  of  the  specimens  which  appear  in  the  ledge  to  be  completely  homo- 
geneous are  in  fact  made  up  of  fragments  in  a  well-defined  matrix.  The 
breceiated  structure  is  almost  universal.  The  fragments  are  mainly  sharp 
edged  and  range  in  size  from  those  of  microscopic  dimensions  to  those 
several  inches  across.  Sometimes  the  disthiction  between  fragments  and 
anatrix  is  difficult  to  make,  since  the  material  of  the  two  is  similar  in  com- 
position and  in  the  coarseness  of  texture.  Usually,  however,  they  are 
distinguished  by  differences  in  color  due  to  the  presence  in  them  of  hema- 
tite, ocher,  and  magnetite  grains,  chlorite,  and  sericite,  or  kaolin  flakes, 
:and  certain  indefinite  greenish  and  brownish  stains  in  different  amounts. 
Occasionally  the  fragments  are  darker  colored  than  the  matrix,  but  usually 
the  reverse  is  the  case.  The  snow-white  varieties  so  characteristic  of  the 
Gogebic  cherts  occur  only  as  fragments  in  the  Randville  breccias.  There 
is  also  frequently  noted  a  difterence  in  texture  between  the  fragments  and 
the  inclosing  matrix.     In  the  fragments  the  texture  is  very  fine,  but  in  the 


ALGONKIAN,  RANDVILLE  DOLOMITE.  229 

matrix  it  is  often  quite  coarse.  Often  the  coarsest  texture  is  in  a  zone 
innnediately  surrounding  the  fragments.  These  coarsest  portions  may  be 
traced  continuously  into  stringers  extending  into  the  fragments  and  often 
separating  them  into  several  portions.  Usually  the  stringers  are  extremely 
narrow,  but  sometimes  they  are  rather  wide.  They  cross  the  fragments  in 
all  directions,  constituting  the  quartz  filaments  and  veins  noticed  in  the 
hand  specimens. 

In  some  specimens  the  filaments  also  cross  the  material  of  the  matrix, 
and  sometimes  little  irregular  areas  of  the  coarsely  textured  aggregate 
occur  in  the  midst  of  the  finer-textured  aggregates,  as  though  they  repre- 
sented cross  and  oblique  sections  through  tiny  quartz  veins.  In  still  other 
cases  the  coarse  quartz  grains  form  little  round  areas  composed  of  a  central 
grain  surrounded  by  a  zone  of  grains  radially  airanged  around  the  nucleal 
grain.  In  short,  the  rocks  look  as  though  they  may  originally  have  been 
nearly  homogeneous  cherts,  containing  here  and  there  a  fragmental  quartz 
grain,  which  were  subsequently  very  thoi'oughly  shattered  and  then  healed 
by  infiltrated  quartz.  Moreover,  they  seem  to  have  been  subjected  to 
thorough  silicification,  so  that  it  is  doubtful  if  in  some  sections  any  of  the 
original  rock  material  remains.  Sections  which  in  natural  light  show 
plainly  the  presence  of  fragments  in  a  matrix,  between  crossed  nicols  appear 
as  a  nearly  homogeneous  mosaic  of  small  quartz  grains  of  uniform  size  and 
character,  interrupted  here  and  there  by  lines  of  coarser  mosaics,  marking 
the  positions  of  quartz  veins. 

CONCLUSIONS    FROM    MICROSCOPICAL    STUDY    AND   COMPARISON'  WITH   SIMILAR  ROOKS    IN  THE    SIARQUETTE 

AND    GOGEBIC    DISTRICTS. 

The  microscopical  features  of  these  cherty  quartz  rocks  are  nearly 
identical  with  those  of  the  cherts  associated  with  the  limestone  in  the 
Gogebic  district,  except  that  forms  composed  of  individualized  quartz 
grains,  with  crystal  outlines,  have  not  been  seen  among  the  Menominee 
rocks.  The  concretionary  structure  that  Irving  and  Van  Hise"  detected 
among  the  Gogebic  cherts  also  seems  to  be  lacking  in  the  Menominee 
ones,  but  this  may  be  due  to  the  few  specimens  that  have  been  seen  that 
are  free  from  brecciation.     In  the  breccias  a  concretionary  arrangement  of 


a  Irving,  R.  D.,  and  Van  Hise,  C.  R.,  The  Penokee  iron-bearing  series  of  Michigan  ami  Wis- 
consion:  Men.  U.  S.  Geol.  Survey,  vol.  19,  1892,  pp.  132-133,  and  PI.  XVI,  tigs.  2,  3,  4. 


230  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

the  quartz  is  sometimes  suggested  in  the  groundmass  surrounding  the 
fragments,  and  occasionally  in  the  fragments  themselves,  but  the  suggestion 
is  h  very  obscure  one. 

The  principal  conclusion  deduced  from  the  study  of  the  cherty  quartz- 
ites  is  to  the  effect  that  they  may  be  regarded  as  intermediate  forms  linking 
the  dolomites  beneath  them  with  the  jaspilites  of  the  Negaunee  formation 
that  must  at  some  time  have  existed  above  them.  While  we  have  no  speci- 
mens of  the  Negaunee  formation  from  this  district,  except  in  the  form  of 
small  pebbles  in  the  basal  conglomerate  of  the  Upper  Huronian,  in  the  Mar- 
quette district  the  Negaunee  formation  is  well  exhibited,"  and  its  cherts  and 
jaspilites  have  been  carefully  studied. 

The  Randville  cherts  are  found  to  have  many  of  tfhe  features  of  these 
rocks,  and  may  well  be  transition  phases  between  them  and  the  underlying 
dolomites.  The  latter  are  in  many  instances  silicified,  and  in  some 
instances  are  so  much  so  that  they  might  well  be  described  as  cherty  dolo- 
mite. However,  these  cherty  forms  are  not  as  common  in  the  Menominee 
district  as  they  are  in  the  Marquette  district. ''  Otherwise  the  dolomites  and 
cherts  of  the  two  districts  are  very  similar,  and  the  words  used  by  Van  Hise 
in  describing  those  of  the  Kona  formation  in  the  Marquette  district  might 
almost  equally  well  be  used  in  the  descrijjtions  of  the  dolomite  and  cherts 
of  the  Randville  series  in  the  Menominee  district.  If  lithological  features 
are  of  any  value  as  criteria  upon  which  to  base  conclusions  as  to  the  strati- 
graphical  continuity  of  formations  in  sedimentary  basins  situated  in  the 
same  general  geological  province,  then  the  identity  of  character  between 
the  dolomite  and  cherts  in  the  Grogebic,  Marquette,  and  Menominee  districts 
must  mean  that  they  are  at  the  same  geological  horizon,  although  their  con- 
tinuity on  the  surface  is  inten-upted  by  wide  stretches  of  younger  sediments. 

ORIGIN   OF   THE   DOLOMITES   AND   CHERTY   QUARTZ   ROCKS. 

From  the  statements  above  made  concerning  the  character  of  the 
dolomites  and  cherts,  it  is  evident  that  their  origin  must  be  the  same  as  the 
origin  of  the  corresponding  rocks  in  the  Grogebic  and  Marquette  districts. 

a  Van  Hise,  C.  R.,  and  Bay  ley,  W.  S.,  The  Marquette  iron-bearing  district  of  Michigan,  with  atlas, 
including  a  chapter  on  the  Republic  trough  by  H.  L.  Smyth:  Hon.  U.  S.  Geol.  Survey,  vol.  28,  1897, 
pp.  370-371. 

''Ibid.,  pp.  248-249. 


AUrONKlAN,  RANDVILLE  DOLOMITE.  231 

Irving  and  Van  Hise"  have  discussed  the  origin  of  the  Grogebic  rocks,  and 
have  reached  the  conclusion  that  there  is  no  definite  proof  as  to  whether 
the  dolomite  is  of  chemical  or  of  organic  origin,  but  that  many  geologists 
would  assert  that  the  very  nature  of  the  rock  precludes  the  possibility  of 
its  having  been  produced  by  other  than  life  agencies.  Where  there  are  no 
fossils,  as  in  these  dolomites,  it  is  at  best  a  matter  of  opinion  as  to  their 
origin,  but  in  making  up  a  judgment  upon  this  point  the  organic  beds  of 
chert  of  later  times  associated  with  limestones  and  the  beds  of  iron  carbon- 
ate and  carbonaceous  material  in  higher  horizons  of  the  series  are  facts  to 
be  taken  into  account.  While  not  expressing  any  definite  opinion  as  to  the 
origin  of  the  dolomites,  the  impression  left  by  the  discussion  is  that  they 
might  well  be  looked  upon  as  organic  deposits. 
As  for  the  cherts,  they  declare  that — 

The  vein-like  character  of  a  part  of  the  chert  impHes  that  the  silica  has  been 
rearranged  to  some  extent,  or  partially  introduced  subsequently  to  the  deposition  of 
the  main  body  of  the  belt.  The  deposition  of  similar  cherty  carbonates  of  great 
thickness  is  definitely  known  to  occur  in  the  Carboniferous  and  Permian''  periods. 
The  chert  is  here  probably  all  of  organic  origin.  Whether  the  chert  in  the 
limestones  under  discussion  is  an  organic  or  a  chemical  substance  it  is  impossible  to 
say ;  but  it  is  certain  that  in  later  time  we  have  the  exact  analogue  of  the  deposits 
described,  which  are  definitely  known  to  be  organic  deposits. 

It  appears  that  the  chert  of  the  limestone  belt,  whether  original  or  secondary, 
had  in  the  main  reached  its  present  condition  before  the  accumulation  of  the  imme- 
diately overlying  formation.  That  the  chert  has  been  rearranged  to  a  greater  or  less 
extent  since  its  deposition,  and  that  in  the  cracks  infiltrating  solutions  have  brought 
additional  silica,  is  more  than  probable. 

Again  in  summarizing  their  conclusions  they  state:" 

The  chert  and  limestone  are  water-deposited  sediments;  whether  chemical  or 
organic  is  uncertain,  but  it  is  not  improbable  that  the.y  are  partly  or  whoUv  the 
latter.  However,  if  this  is  the  case,  the  silica  has  subsequently  changed  to  the 
mineral  form  [quartz],  and  has  been  extensively  rearranged,  while  the  limestone  has 
become  dolomitized. 


«Mon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  pp.  140-141. 

6Hinde,  G.  J.,  On  the  organic  origin  of  tlie  chert  in  the  Carboniferous  limestone  series  of  Iceland 
and  its  similarity  to  that  in  the  corresponding  strata  in  North  Wales  and  Yorkshire:  Geol.  Mac. 
London,  new  series,  decade  3,  vol.  4,  pp.  435-446.     Also  on  the  chert  and  siliceous  schists  of  the 
Permo-Carboniferous  strata  of  Spitzbergen,  and  on  the  characters  of  the  sponges  therefrom,  which 
have  been  described  by  Dr.  R.  von  Dunikowski:  Idem,  vol.  5,  pp.  241-251. 

"Mon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  p.  142. 


232  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

These  words  are  so  entirely  applicable  to  the  Randville  cherts  and 
dolomites  that  they  have  been  quoted  here,  partly  as  a  summary  of  the 
conclusions  that  must  be  arrived  at  after  studying  these  rocks,  and  partly  to 
emphasize  the  fact  that  what  is  true  of  the  dolomite  formation  in  the  Gogebic 
district  is  true  also  of  the  corresponding  formation  in  the  Menominee  dis- 
trict. The  two  formations  are  almost  identical  in  all  their  characteristics. 
There  can  be  little  doubt  that  they  represent  dissevered  parts  of  a  formation 
that  once  extended  continuously  over  both  districts. 

FOLDING. 

A  knowledge  of  the  folds  of  the  Randville  dolomite  is  the  key  to  the 
knowledge  of  the  folding  of  the  entire  series  of  Algoukian  rocks  in  the 
district.  Moreover,  the  distribution  of  the  folds  determines  the  distribution 
of  the  productive  ore  bodies,  as  will  be  shown  later.  Consequently  it 
is  necessary  to  study  the  folding  of  this  formation  with  some  minuteness  in 
order  that  a  better  understanding  may  be  had  of  the  conditions  which  have 
made  the  district  of  such  economic  importance. 

The  formation,  as  can  easily  be  discerned  from  its  mapped  distribution 
(PI.  IX),  occurs  in  two  anticlines  and  three  synclines  in  the  western  portion 
of  the  district  and  two  synclines  and  one  anticline  in  its  eastern  portion. 
Structurally  the  northern  belt  of  dolomite  is  a  southward-di2:)ping  monocline. 
The  central  and  southern  belts  are  anticlines.  Between  the  belts  are  syn- 
clines. South  of  the  southern  belt  is  a  syncline,  on  the  southern  limb  of 
which  one  would  expect  to  find  a  belt  of  dolomite.  This  belt  might  be 
expected  to  appear  above  a  belt  of  Sturgeon  quartzite,  both  overlying  the 
Quinnesec  schists  of  tlie  Menominee  River.  Apparently,  however,  the 
quartzite  and  limestone  were  not  deposited,  or  both  have  been  completely 
removed  by  erosion  during  inter-Menominee  time,  so  that  the  formations  of 
the  Upper  Menominee  series  lie  upon  the  greenstone-schists  (see  map  and 
structure  section  AA,  PI.  IX). 

MAJOR   FOLDING. 

From  the  mapped  distribution  of  the  dolomite  formation  (PI.  IX)  and 
its  relations  to  the  iron  formation  (see  p.  251),  it  is  clear  that  the  central 
and  southern  belts  are  two  anticlines  with  axes  striking  a  little  north  of 
west,  connected  with  one  another  by  a  syncline,  and  that  a  syncline  also 
connects  the  central  belt  with  the  northern  one. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  233 

In  the  central  belt  the  northern  and  southern  borders  of  the  formation 
are  known  accurately  only  in  the  neighborhood  of  the  Indiana  mine. 
Just  south  of  the  Cuff  mine  shaft  the  dip  of  the  dolomite  is  about  2.5°  N. 
At  the  Indiana  mine,  near  the  southern  border  of  the  belt,  the  dip  of  the 
upper  contact  of  the  dolomite  is  south  at  an  angle  of  about  60°,  but,  if 
the  evidence  of  drill  holes  is  to  be  relied  upon,  the  dip  flattens  at  greater 
depths.  West  of  the  Cuff  mine  are  a  number  of  ledges  situated  near  the 
center  of  the  belt  whose  bedding,  as  well  as  can  be  determined,  is  vertical. 
Thus  the  dips  in  this,  the  only  portion  of  the  central  belt  that  can  be 
examined  across  the  strike  from  its  southern  to  its  northern  contacts,  are  in 
accordance  with  the  view  that  the  belt  is  structurally  an  anticline. 

The  southern  belt  over  much  of  its  extent  presents  the  appearance  of 
a  uniform  succession  of  isoclinal  beds — i.  e.,  it  appears  as  a  monocline.  In 
its  western  portion  near  the  Chapin  mine  the  dips  of  the  beds  exposed  on 
the  surface  are  uniformly  at  high  angles  to  the  north. 

Farther  east,  in  the  neighborhood  of  the  line  between  sees.  32  and  33, 
T.  40  N.,  R.  30  W.,  they  are  high  to  the  south.  In  the  longitude  of 
Quinnesec  they  are  high  to  the  north  in  the  southern  half  of  the  belt  and 
high  to  the  south  in  its  northern  half.  East  of  this  longitude  the  dips 
are  uniformly  to  the  south  except  where  minor  folds  are  encountered,  but 
the  angle  of  dip  becomes  flatter  and  flatter  as  we  proceed  eastward.  NeaL- 
the  Sturgeon  River  it  rarely  exceeds  55°. 

Consideration  of  these  dips  indicates  that  the  southern  anticline  is  a 
very  closely  compressed  fold  with  a  warped  axial  plane.  At  its  western 
end  this  plane  is  overturned  to  the  south;  a  little  farther  east  it  is  over- 
turned to  the  north;  in  the  longitude  of  Quinnesec  the  fold  appears  to  be 
fan  shaped,  and  at  its  eastern  end  it  is  again  overturned  to  the  north. 


CROSS   FOLDING. 


The  attitude  of  minor  folds  is,  as  is  well  known,  an  indication  of  the 
attitude  of  the  major  folds  on  which  they  are  superimposed.  By  using  this 
principle  it  is  concluded  that  the  major  anticlines  in  this  district  disappear 
to  the  east  and  to  the  west  by  plunging  beneath  the  Upper  Menominee 
sediments.  Detailed  examination  of  the  ends  of  the  anticline  north  of 
Lakes  Antoine  and  Fumee  seems  to  show  that  this  belt  does  actually 
disappear  in  this  way,  and  the  sudden  disappearances  of  the  southern  belt 


234  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

toward  the  west  points  to  a  similar  conclusion  with  respect  to  its  termination 
in  this  direction. 

The  most  easterly  exposures  of  the  central  belt  are  at  Iron  Hill  in  sec. 
32,  T.  40  N.,  R.  29  W.  Most  of  the  width  of  the  belt  in  this  neighborhood 
is  covered  by  the  Lake  Superior  sandstone,  but  at  the  southwest  margin  of 
the  sandstone  covering-  abundant  exposures  of  the  dolomites  occur.  Their 
bedding  is  very  distinct,  with  a  definite  strike  N.  50°  to  60°  W.  This 
strike  projected  southeastwardly  would  carry  the  dolomite  into  a  well- 
characterized  area  of  ferruginous  chert  and  slates.  These  slates  and  cherts 
are  above  the  dolomite,  hence  the  latter  rock  must  plunge  under  them  on 
its  line  of  strike.  Corroborative  evidence  for  this  conclusion  is  found  in 
the  fact  that  the  easternmost  exposure  of  the  dolomite  formation  consists  of 
dolomitic  cherts.  These  rocks  not  only  limit  the  normal  dolomite  to  the 
east,  but  they  are  found  also  wrapping  around  the  en^d  of  the  hill  and 
appearing  again  in  the  southeast  side  and  along  the  southern  side  of  the 
dolomite  exposures  (see  PI.  XVII,  A).  Where  its  relations  to  the  normal 
dolomite  can  be  seen,  the  chert  clearly  overlies  the  latter.  In  other  portions 
of  the  district  where  it  is  exposed,  it  is  likewise  seen  to  be  above  the  normal 
dolomite.  Since,  then,  the  uppermost  layers  of  the  dolomite  formation  at 
Iron  Hill  are  the  last  to  disappear  to  the  east,  the  formation  must  be 
terminated  by  an  eastward-plunging  anticline. 

At  the  west  end  of  the  belt  the  conditions  are  very  unfavorable  for 
determining  the  method  of  its  disappearance  in  this  direction.  The  west- 
ernmost place  to  which  the  formation  is  known  to  extend  is  in  the  tunnel  and 
drill  hole  near  the  quarter  post  between  sees.  20  and  21,  T.  40  N.,  R.  30  W., 
on  the  south  side  of  the  great  hill  overlooking  Lake  Antoine.  This  hill,  like 
nearly  all  of  the  other  higher  elevations  in  the  district,  is  covered  with  sand- 
stone, so  that  the  areal  distribution  of  the  dolomite  in  this  neighborhood  can 
not  be  determined.  The  west  and  northwest  slopes  of  the  hill,  however, 
are  broken  by  the  mining  and  exploration  pits  of  the  Cornell,  the  Traders, 
and  Cliiford  mines,  so  that  the  extension  of  the  dolomite  in  this  direction 
is  impossible.  Moreover,  the  magnetic  observations  in  sec.  20  indicate  that 
this  section  is  underlain  by  a  broad  area  of  the  iron-formation  rocks.  These 
facts  seem  to  show  that  the  west  end  of  the  central  dolomite  belt,  like  its 
east  end,  must  terminate  in  an  anticline  which,  in  this  case,  pitches  to  the 
west. 


U.   S.   GEOLOGICAL    SURVEY 


MONOGRAPH    XLVI       PL.    XVII 


,-1.      FOLD    \N    UHERT    AT    IRON    HILL    IN    SEC,    32,   T.   40   N.,    R.   29   W. 
The  underlying  rock  is  a  conglomerate  dolomite  like  tliat  shown  in  PI,  XVI,  B.     The  overlying  chert  is  brecciated. 


B.     SMALL   FOLDS    IN    TRADERS  JASPILITE,    WEST   SIDE   OF   CLIFFORD    PIT,   TRADERS   MINE. 

The  rocks  are  brecciated,  but  folds  can  nevertheless  be  plainly  recognized  in  them.      In  the  view  one  anticline  and  one  syncline  can  easily  be 

TT.ade  out. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  285 

The  behavior  of  the  ends  of  the  southern  anticHne  can  not  be  described, 
since  both  are  covered  with  sandstone  and  drift.  But  for  this  belt,  the 
evidence  of  the  minor  folds  is  fairly  conclusive,  so  that  it  appears  safe  to 
assume  that  this  dolomite  plunges  below  the  Upper  Menominee  rocks. 
The  westernmost  point  at  which  the  dolomite  is  known  to  occur  is  near 
the  center  of  sec.  25,  T.  40  N.,  R.  31  W.,  where  it  was  reached  by  a 
drift  running  about  50  feet  north  from  the  bottom  of  a  shaft  located  150 
feet  southwest  of  the  center  of  the  section  (fig.  16).  The  dolomite  lies  to 
the  north  of  a  slate  and  ore  formation  and  is  overlain  unconformably  by  the 
Lake  Superior  sandstone.  The  dip  of  the  dolomite  is  apparently  to  the 
south,  but  the  surface  on  which  the  sandstone  was  deposited  slopes  to 
the  north.  Unfortunately  we  are  here,  as  at  other  important  places,  met 
by  the  sandstone  covering  which  completely  hides  from  view  the  relations 
of  the  rocks  beneath  it.  From  the  magnetic  observations  made  on  the 
west  slope  of  the  hill  and  in  the  valley  of  the  Menominee  at  the  base  of  this 
slope  it  appears  that  the  iron  formation  occupies  a,  large  part  of  the  area 
between  the  hill  and  the  river  and  nearly  surrounds  its  west  end.  At  its 
east  end  the  southern  belt  is  covered  completely  by  Paleozoic  beds,  so  that 
the  manner  of  its  disappearance  with  respect  to  the  Upper  Huronian  sedi- 
ments is  not  known. 

From  the  above  statements  it  is  clear  that  in  addition  to  the  major  east- 
west  anticlines  and  synclines  that  are  so  prominent  in  the  district  the 
dolomite  formation  is  also  affected  by  a  gentle  but  large  anticlinorium  with 
axis  running  approximately  north-south. 

MINOR    FOLDING. 
THK   NORTHERN   BELT. 

In  the  northern  belt  minor  folding,  if  it  exists,  can  not  be  discovered 
except  at  the  extreme  western  end,  where  the  belt  makes  the  turn  northward 
into  the  Calumet  trough  (see  p.  189).  The  area  occupied  by  the  belt  is 
included  within  the  valley  of  Pine  Creek.  Throughout  nearly  its  entire 
extent  the  rock  is  buried  beneath  the  valley  sands.  The  few  exposures 
belonging  to  it  exhibit  no  evidence  of  folding. 

THE  CENTRAL  BELT. 

In  the  central  belt  the  exposures  are  almost  uniformly  low,  massive 
ledges,  in  which  strikes  and  dips  are  not  always  easy  to  obtain.     Where 


236 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


observations  were  taken  the  strike  is  invariably  in  the  direction  of  the 
trend  of  the  belt.  West  of  the  Cuff  mine  the  dips  are  practically  vertical, 
and  the  belt  appears  to  be  isoclinal.  East  of  the  Indiana  mine  the  dips  are 
i;sually  70°  to  80°  S.  But  here  only  the  southern  side  of  the  belt  is  open 
to  inspection,  since  the  northern  side  is  buried  under  sandstone.  At  the 
Cuff  mine  test  pits  show  that  the  northern  boundary  of  the  dolomite  swings 
suddenly  to  the  north,  and  a  dolomite  ledge  exposed  at  the  southwest  end 


€ls    = 

LEGEND 
Lake  Superior  sandstone                         o'*''^ 

■eis 

J       = 
s      = 
d      = 

°0 

Jaspilite  (Traders) 

Slate  (Traders  or  Randville ) 

Randville  dolomite 

Test  pits 

/OS 

o 

Mining  pits 

•<- 

Contact  line                                                                             ^ 
,'o\               o'                o                  ( 

\    ^      \                                                                                        1 
^            N                                          ,'~-v      .1      ^1        / 

J                      o 

S 

_   Dolomite  ledge  about 
200  paces  west 

scale:    1    INCH  =  BO  PACES 

°J 

Dolomite  ledges     ,^^ 
250  paces  south  and  ^ 
800  east 

Fig.  17.— Sketch  plan  of  Cuflf  mine  and  vicinity. 


N.     There 


of  the  open  pit  east  of  the  shaft  strikes  east-west  and  dips  45^ 
is  here  plainly  a  small  subordinate  anticline  (fig.  1 7). 

At  Iron  Hill,  at  the  eastern  extremity  of  the  belt,  there  is  also  clear 
evidence  of  minor  folding.  Near  the  east  quarter  post  of  sec.  32,  T.  40  N., 
R.  29  W.,  are  two  small  knolls  of  dolomitic  chert  separated  by  a  small  valley. 
The  rock  in  the  northern  knoll  dips  75°  to  90°  S.  Across  the  valley,  and  at 
a  distance  of  only  about  50  feet,  the  rock  on  the  northern  side  of  the  south- 
ern ledge  dips  45°  N.     On  the  soutliern  side  of  the  same  knoll  the  dip 


ALGONKIAN,  RANDVILLE  DOLOMITE.  237 

is  45°  S.  The  dips  of  the  beds  in  the  great  ledges  of  dolomite  farther 
south  are  85°  to  86°  S.  There  are  here,  then,  at  least  one  minor  syncline 
and  two  anticlines,  superimposed  on  the  major  antichne  that  gives  rise  to 
the  belt  (see  map,  PI.  XLII). 

The  southern  boundary  of  the  dolomite  in  places  terminates  in  little 
chffs.  One  of  these  is  situated  500  paces  west  of  the  east  line  of  the  sec- 
tion. The  face  of  the  cliff  consists  of  white  cherty  quartzite,  under  which 
is  a  much-jointed,  conglomeratic  or  brecciated  dolomite.  A  side  view  of 
the  cliff  (see  PI.  XVII,  A)  shows  the  chert  extending  vertically  up  its  face 
to  the  top  and  then  suddenly  bending  northward  and  becoming  horizontal 
and  covering  the  dolomite  with  a  distinct  layer  which  finally  disappears 
under  the  soil.  The  photograph  also  shows  plainly  that  not  only  does  the 
chert  roll  over  the  dolomite  but  that  it  is  further  folded  into  crumples  of 
small  dimensions.  The  intensity  of  the  folding  at  this  place  is  also  indi- 
cated by  the  brecciated  character  of  the  chert.  Here  the  folding  is  no 
doubt  connected  with  the  existence  of  the  pitching  anticline  which  carries 
the  dolomite  beneath  the  Hanbury  slates. 

THE  S(>i:ther\'  belt. 

MARGINAL    FOLDS. 

The  southern  belt  appears  to  be  practically  isoclinal  throughout  nearly 
its  entire  exposed  extent.  Nevertheless  close  folding  may  be  observed  in 
a  number  of  places.  Minor  folding  is  abundantly  exhibited  on  the  south 
side  of  the  formation,  where  it  is  in  contact  with  the  overlying  iron  forma- 
tion. The  numerous  synclines  found  here  afforded  suitable  conditions  for 
the  concentration  of  the  ores,  and  it  is  in  them  that  the  larger  mines  are 
situated.  The  mining  operations  have  brought  to  our  knowledge  the 
underground  relations  of  the  two  formations  so  fully  that  the  nature  of  the 
folds  in  them  has  been  made  very  clear.  The  most  important  ones  may 
be  named  from  the  mines  occupying  them  as  follows:  The  Walpole,  the 
Pewabic,  the  Quinnesec,  the  Norway,  the  Aragon,  and  the  West  Vulcan.  All 
of  these  are  closely  compressed  folds  pitching  to  the  west  at  angles  varying 
between  25°  and  80°,  usually  becoming  flatter  at  greater  and  greater 
depths.  The  western  folds  are  overturned  to  the  south  and  the  eastern 
ones  to  the  north.  The  axial  planes  of  the  Walpole  and  the  Pewabic  folds 
dip  about  70°  N.  and  that  of  the  Quinnesec  fold  60°  in  the  same  direction, 


238  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

while  the  Norway  fold  dips  70°  S.,  the  Aragou  fold  60°  S.,  and  the  West 
Vulcan  fold  is  nearly  vertical.     Although  these  folds  are  discussed  rather 
fully  in  connection  with  the  description  of  the  ore  deposits,  a  brief  summary  • 
of  the  evidence  upon  which  their  recognition  is  based  may  conveniently  be 
given  in  this  place. 

Walpole  fold. — The  most  westerly  fold  whose  existence  is  made  certain 
by  mining  operations  is  that  in  which  the  Chapin,  Millie,  and  the  Wal- 
pole ore  deposits  are  found.  This  is  not  anywhere  to  be  seen  on  the 
surface,  since  the  Lake  Superior  sandstone  and  the  loose  materials  of 
the  drift  cover  all  the  ground  in  its  vicinity.  The  existence  of  the  fold, 
however,  is  well  established  by  the  underground  working  of  the  Walpole 
mine,  the  old  shaft  (No.  1)  of  this  mine  being  on  its  north  limb,  and 
the  southern,  or  No.  2,  shaft  on  its  southern  limb  (fig.  34).  The  dolomite 
has  not  been  met  with  in  No.  1  shaft,  and  no  crosscuts  have  been  driven 
to  the  north  from  this  shaft  to  locate  it.  About  550  feet  to  the  west, 
however,  is  the  A  shaft  of  the  Chapin  mine,  and  110  feet  north  of  this  on 
the  surface  is  the  southern  limit  of  the  dolomite.  The  dolomite  is  again 
met  with  at  the  east  end  of  the  third  level  of  the  Walpole,  at  a  point  1,625 
feet  east  and  525  feet  south  of  the  shaft.  Just  before  reaching  the 
dolomite  the  drift  encountered  a  light-colored  slate  known  to  occur  else- 
where at  the  base  of  the  Traders  formation.  This  rock,  varying  somewhat 
in  appearance,  but  nevertheless  essentially  the  same  in  composition,  is 
disclosed  again  at  several  points  at  the  ends  of  crosscuts  running  north 
from  the  main  drift.  The  dolomite  is  immediately  behind  this.  The 
Traders  slate  is  again  found  at  the  end  of  a  south  crosscut  at  1,425  feet 
east  and  475  feet  south  of  the  shaft,  and  the  same  slate,  underlain  by  a 
naiTOW  bed  of  quartzite  (Traders  quartzite),  back  of  which  is  the  dolomite,  • 
occurs  again  900  feet  east  and  425  feet  south  of  the  shaft.  These 
exposures  outline  a  narrow  syncline  of  dolomite  pitching  to  the  west.  No. 
2  shaft  is  a  little  over  1,000  feet  south  of  shaft  No  1.  South  of  it  on  the 
third  level  the  quartzite  that  is  so  frequently  associated  with  the  dolomite 
again  appears,  and  at  a  point  375  feet  east  of  the  shaft  the  east  end  of  a 
drift  terminates  in  the  same  rock.  No  other  indications  of  the  presence  of 
the  dolomite  are  met  with  on  the  third  level,  but  in  a  long  crosscut  running 
north  from  the  southern  shaft  and  connecting  it  with  the  workings  of  the 
northern   shaft,  at  a  place  midway  between  the  two,  three   belts  of  ore- 


AL(;ONKIAN,  RANDVILLE  DOLOMITE.  239 

bearing  material  are  uncovered,  like  the  material  lying  above  the  Traders 
slate  and.  quartzite  elsewhere  in  the  mine.  The  inference  is  plain  that  the 
dolomite  lies  a  short  distance  to  the  east  of  this  crosscut,  and  that  its 
border  is  crenulated.  Further,  it  is  evident  that  the  dolomite  mu.st  form 
an  anticline  between  the  syncline  in  which  the  workings  of  the  northern 
shaft  are  developed  and  another  syncline  partly  outlined  by  the  exposures 
in  the  workings  of  the  southern  shaft.  The  Walpole  fold  is  thus  composed 
of  two  synclines  and  an  intermediate  anticline.  The  folds  pitch  to  the 
west  and  dip  to  the  north. 

Pewahic  fold. — The  Pewabic  fold,  like  the  Walpole  fold,  has  been 
developed  solely  by  underground  work  (fig.  35).  Dolomite  was  reached  at 
the  end  of  a  crosscut  running  a  little  east  of  north  from  No.  1  shaft  of  the 
Pewabic  mine,  at  the  first  level,  and  at  a  distance  of  870  feet  from  the 
shaft.  This  point  is  about  1,250  feet  east  and  about  150  feet  south  of  the 
Walpole  shaft  No.  2,  just  south  of  which,  as  was  stated  in  the  j^receding 
paragraph,  dolomite  was  found.  There  is  then  an  anticline  of  this  rock 
between  the  Walpole  and  the  Pewabic  basins.  The  latter  basin  is  further 
outlined  by  the  discovery  of  dolomite  by  means  of  two  drill  holes  put  in  to 
the  north  and  the  south  from  the  east  end  of  the  third  level  of  the  Pewabic 
mine,  and  a  third  hole  driven  to  the  south  from  the  drift  extending  south- 
ward from  the  same  level,  about  500  feet  east  of  shaft  No.  1.  Normal 
dolomite  was  not  encountered  in  this  drill  hole,  but  the  drill  ended  in  the 
Traders  quartzite,  which  is  found  only  in  close  association  with  this  rock. 
On  the  sixth  level,  however,  a  hole  drilled  in  the  same  direction  reached 
the  dolomite.  The  east  end  of  the  fold  is  complicated  by  a  fault  the  exact 
character  of  which  has  not  been  worked  out.  By  these  explorations  it  is 
shown  that  the  iron  formation  of  the  Pewabic  mine  and  the  rocks  associated 
with  them  lie  in  a  syncline  of  the  dolomite  which  widens  to  the  west.  The 
mining  operations  show  that  the  pitch  is  to  the  west  and  the  dip  of  the  fold 
to  the  north. 

Quinnesec  fold. — The  underground  workings  of  the  Quinnesec  and 
the  Cundy  mines  have  not  yet  reached  the  typical  dolomite  on  either 
side  of  the  ore  formation,  though  its  presence  north  of  the  Quinnesec  int  is 
indicated  by  the  nature  of  the  rocks  met  with.  The  principal  evidence  we 
have  of  the  existence  of  a  fold  here  is  found  on  the  surface  (PI.  XXX). 
Near  the  corner,  between  sees.  34  and  35,  T.  40  N.,  R.  30  W.,  and  sees.  2 


240  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

and  3,  T.  39  N.,  R.  30  W.,  is  a  large  ledge  of  well-bedded  dolomite  with  a 
dip  of  80°  S.  and  a  strike  N.  70°  W.  This  dolomite,  if  continued  along 
its  strike,  would  pass  through  the  large  open  pit  of  the  Quinnesec  mine, 
in  which  the  ore  formation  is  well  exposed.  Exposures  of  the  dolomite 
occur  as  far  west  as  the  road  running  north  to  the  Indiana  mine,  and  it  is 
found  again  in  the  Quinnesec  public  well,  situated  about  750  feet  west  of 
the  corner.  The  strike  of  the  dolomite  beds  projected  beyond  this  point 
would  carry  them  south  of  the  Quinnesec  mine  into  an  area  dotted  with 
ledges  and  test  pits  in  the  jaspers  and  slates  of  the  iron  formation. 

North  of  the  well  there  are  no  exposures  of  the  dolomite  for  300  paces 
(about  780  feet),  though  a  drill  hole  put  down  about  525  feet  east  of  the 
Quinnesec  shaft  disclosed  the  rock  under  the  surface  about  250  feet  south 
of  the  southernmost  exj^osure.  North  of  this  drill  hole  exposures  are  found 
at  short  intervals  for  1,000  feet,  and  then  at  greater  intervals  for  2,500  feet 
beyond.  The  beds  in  the  southern  ledges  strike  from  3°  to  8°  north  of 
west  and  dip  nearly  vertically. 

Between  the  well  that  marks  the  westernmost  point  at  which  the 
dolomite  lias  been  found  south  of  the  mine  and  the  next  most  southern 
occurrence  of  the  same  rock  is  a  valley  530  feet  wide  in  which  no  exposures 
of  any  kind  are  found.  Artificial  openings,  however,  show  that  the  valley 
is  occupied  by  the  slates  and  other  rocks  of  the  iron  formation.  The 
displacement  of  the  dolomite  is  thus  a  little  over  500  feet.  A  glance  at  the 
geological  map  (PI.  XXX)  will  make  these  relations  plain.  This  displace- 
ment must  be  due  either  to  a  fault  trending  a  little  east  of  north  or  to  a 
syncline  pitching  west.  Since  there  is  no  direct  evidence  of  a  fault  at  this 
place,  nor  in  the  dolomite  beds  almost  continuously  exposed  a  short  distance 
east  of  the  section  line,  and  since  faults  of  important  dimensions  are  not 
common  elsewhere  in  the  district,  it  is  concluded  that  the  displacement 
must  be  due  to  folding.  The  dolomite  ledge  near  the  corner  is  at  the  crest 
of  an  anticline.  The  dolomite  north  of  the  mine  is  the  south  side  of  another 
anticline,  and  the  interval  between  is  occupied  by  a  synclinal  trough  filled 
with  iron  formation  rocks. 

Norway  fold. — The  folds  in  which  the  Norway  and  the  Aragon  mines 
are  situated  are  as  well  known  as  any  others  in  the  district  because 
of  their  extensive  exploration  by  mining  operations.  On  the  surface  a 
ledge  of  dolomite  exists  near  the  corner  between  sees.  4,  5,  8,  aiid  9,  and 


ALGONKIAN.  RANDVILLE  DOLOMITE.  241 

four  other  ledges  of  the  same  rock  are  exposed  nortlieast  of  this  one,  i.  e., 
in  the  southeast  quarter  of  the  southeast  quarter  of  sec.  4,  T.  39  N.,  R.  29 
W.  (see  PI.  XXXI).  On  the  north,  south,  and  west  of  these  exposures 
the  iron  formation  is  known  to  occur.  There  is,  consequently,  an  anticline 
of  dolomite  between  the  northern  area  of  the  iron  formation,  which  is  the 
basin  of  the  Norway  deposits,  and  the  southern  area,  in  which  the  Aragon 
deposits  lie.  The  two  folds — the  Norway  and  the  Aragon — are  comparable 
with  the  Walpole-Pewabic  folds  farther  west.  The  analogy  is  all  the  more 
striking  since  the  Norway  fold,  like  the  Walpole,  is  a  double  syncline 
pitching  to  the  west. 

The  northern  side  of  the  Norway  syncline  is  quite  sharply  delimited 
on  the  surface  by  a  number  of  dolomite  exposures  stretching  for  a  distance 
of  about  1,400  feet  along  a  line  running  about  N.  77°  W.  immediately 
north  of  the  great  open  pits  of  the  Norway  and  Perkins  mines. 

The  south  limb  of  the  fold  is  indicated  by  the  exposures  in  the 
southeast  quarter  of  sec.  4,  alread}^  referred  to.  To  the  east  of  the  mine 
the  country  for  some  distance  is  sand  covered,  and  there  are  no  pits  nor 
mine  openings  that  yield  information  as  to  the  nature  of  the  underlying 
rock.  Consequently  the  eastern  limit  of  the  fold  can  not  be  designated 
with  any  close  degree  of  accuracy.  A  diamond  drill  located  about  1,000 
feet  north  of  the  south  quarter  post  of  sec.  4,  however,  encountered 
■dolomite.  Since  this  hole  is  nearly  on  the  strike  of  the  iron  formation  as 
exposed  in  the  Norway  and  the  Perkins  pits,  it  is  plain  that  this  must 
terminate  to  the  east  befoi'e  the  position  of  the  drill  hole  is  reached. 

In  the  underground  workings  of  the  Norway  mine  the  syncline  is 
beautifull}^  disclosed,  and  it  is  by  means  of  the  mine  explorations  that  we 
discover  the  syncline  to  be  compound.  At  a  number  of  places  drifts  and 
shafts  have  penetrated  the  dolomite  or  the  slates  that  lie  immediately  above 
it.  On  the  north  side  of  the  mine  the  upper  contact  of  the  dolomite  dips 
south  at  angles  varying  between  45°  and  65°.  At  the  bottom  of  the  mine 
the  dips  are  flat  for  short  distances  and  then  on  the  south  side  of  the  ore 
basin  they  become  northerly  at  steep  angles  (see  sections  on  PL  XXXII 
and  fig.  18).  The  anticline  thus  formed  nowhere  reaches  the  surface, 
though  its  apex  sometimes  reaches  a  height  of  100  feet  or  more  above  the 
bottom  of  the  syncline.  On  the  south  side  of  the  anticline  the  dolomite 
falls  rapidly  to  the  south  and  rises  again  in  the  anticline  separating  the 

MON  XLVI — 04 16 


242 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


Norway  and  the  Aragon  ore  Dasins.     This  southern  portion  of  the  Norway 

fold,  which  may  be  designated  as  the  Cy- 
clops syncline,  has  not  yet  been  thoroughly 
explored,  but  we  know  that  its  north  side  at 
one  place  dips  60°  S. 

An  inspection  of  the  cross  sections  of 
^  the  Norway  syncline  will  show  that  it  differs 
g  from  the  more  westerly  folds  in  that  its  axial 
s;  plane  is  either  vertical  or  has  a  high  dip  to 
i^  the  south.  The  character  of  the  Cyclops  syn- 
■^  cline  in  this  respect  is  not  known,  although 
;  it  probalily  also  dips  southward.  The  Nor- 
5  way  fold  must  be  a  double  east-west  syn- 
I  cline,  pitching  to  the  west  and  in  general 
«•  dipping  slightly  to  the  south. 
I  But  the  fold  is  not  simply  a  pair    of 

I  westward-plunging  synclines.  It  is  also 
^  gently  folded  along  a  north-south  axis.  A 
\.  longitudinal  section  through  the  Norway  pit 
5  (fig.  19)  shows  the  dolomite  rising  under  No. 
I  8  shaft  as  a  fiat  ridge  and  sloping  down  into 
:  vallevs  to  the  east  and  the  west.  It  has  been 
I  followed  to  the  east  until  it  again  begins  to 
i  rise  in  an  anticline,  but  has  not  been  traced 
5  to  the  surface.  To  the  west  it  has  been  fol- 
\  lowed  only  sufficiently  far  to  show  that  the 
i  dip  of  its  upper  contact  is  westward  beyond 
I  the  point  at  which  it  is  flat. 

Aragon  fold. — The  anticline  of  dolomite 
Z  near  the  corner  of  sees.  4,  5,  8,  and  9,  already 
^  referred  to,  separates  the  Norway  fold  on  its 
northern  side  from  a  southern  fold  in  which 
lies    the    ore    body    of    the   Aragon    mine. 
Although  not  developed  on  the  surface,  this 
fold  has  been  so  thoroughly  explored  by  the 
lower  workings  of  the  Aragon  mine  that  the 
minutest  details  of  its  structure  at  these  depths  are  known.     Like  the  Nor- 


ALGONKIAN,  RANDVILLE  DOLOMITE. 


243 


way  fold,  the  Aj-agoii  fold  is  also  double,  consisting  of  two  synclines  with 
an  anticline  between  (see  fig.  18).    The  northern  syncline  is,  however,  much 


Lake   Superior  ; 
sandstone    : 


East 


Scale 

440 


DU'-' 


CT- 


880  feet 


Fig.  19.— Longitudinal  section  through  the  Norway  pit,  showing  position  of  dolomite  beneath  the  ore.    Only  the  bottoms 

of  the  shafts  and  lowermost  galleries  are  shown. 

larger  than  the  southern  one,  which,  measured  from  the  crest  of  the  anti- 
cline north  of  it,  is  only  100  feet  in  depth.     The  northern  syncline  is  narrow. 


/;-/ 

,;v 

/Vo 

/////■' 

% 

i§ 

■^--^- 

ill.. 

,-"■■■  •^ 

'iv"^-~r-'"-^" 

Fig.  20.— Horizontal  section  of  the  Aragon  mine  at  the  fifth  level. 

but  its  depth  exceeds  800  feet.     Both  synclines  are  overturned  to  the  north, 
the  dip  of  their  axial  planes  being  about  70°  S.     Typical  dolomite  is  rarely 


244 


THE  MENOMINEE  IKON-BEARING  DISTRICT. 


observed  in  tlie  mine  workings,  but  in  its  place  is  a  talc-schist  into  which 
the  dolomite  seems  to  be  altered  on  and  near  its  contact  with  the  overlying 
rocks.  If  this  schist  is  an  altered  product  of  the  dolomite,  its  contact  with 
the  overlying-  rocks  delimits  the  dolomite  sj^ncline. 

The  plan  of  the  fifth  level  of  the  mine  exhibits  a  good  horizontal  sec- 
tion through  the  northern  syncline  and  the  anticline  separating  this  fold 
from  the  southern  one  (see  fig.  20).  The  plan  of  the  sixth  level  (see  fig.  21) 
shows  in  addition  an  apparently  isolated  mass  of  talc-schist,  separated  by 
ore  from  a  more  northerly  mass  of  the  same  rock,  which  is  plainly  a  lower 


Talc-schist 
(Randuille  formation) 


No. 2  SHAFT 


Fig.  21.— Horizontal  section  ot  the  Aragon  mine  at  the  sixth  level. 


portion  of  the  anticline  cut  on  the  fifth  level.  On  the  seventh  and  lower 
levels  this  mass  is  found  to  be  joined  with  the  main  portion  of  the  schist, 
and  the  intervening  ore  has  disappeared.  The  isolated  area  of  schist  on  the 
sixth  level  is  thus  a  section  through  the  upper  2:>ortion  of  a  dome-shaped 
mass  of  the  schists  that  is  united  with  the  schist  to  the  north  and  that  to  the 
east  by  synclines. 

Projecting  upward  the  contact  of  the  schist  with  the  iron  formation 
north  of  No.  1  shaft,  along  a  line  whose  direction  corresponds  to  the  average 
dip  of  this  contact  below  the  fifth  level,  we  find  the  north  side  of  the  north- 
ern syncline  reaching  the  rock  surface  about  75  feet  below  the  top  of  the 


ALGONKIAN,  BANDVILLE  DOLOMITE.  245 

drift  covering  at  a  point  about  400  feet  south  of  the  north  section  line  of 
sec.  9.  The  southern  side  of  the  fold  does  not  reach  the  surface.  Its  top, 
that  is,  the  apex  of  the  anticline,  is  at  a  depth  of  about  375  feet.  To  the 
west  it  is  deeper,  and  to  the  east  it  becomes  shallower. 

The  southern  fold,  as  has  been  said,  has  a  vertical  dimension  of  only 
about  80  feet.  Its  northern  limb  is  formed  by  the  anticline  just  referred 
to.  Its  southern  limb  is  formed  by  another  anticline,  whose  apex  is  about 
120  feet  south  of  that  of  the  more  northerly  one  and  a  few  feet  lower. 
The  relation  of  these  anticlines  and  synclines  are  well  shown  on  the  cross 
sections  of  the  mine  reproduced  in  fig.  18  and  PI.  XXXII. 

In  attempting  to  define  the  eastern  extension  of  the  Aragon  folds  on 
the  surface  we  are  met  by  the  same  difficulties  as  were  encountered  in 
attempting  to  define  the  eastern  end  of  the  Norway  fold.  At  about  750  feet 
east  of  No.  1  shaft,  however,  a  series  of  great  ledges  of  dolomite  begins  and 
runs  eastward  continuously  for  over  1,000  feet  (see  PI.  XXXIII).  Hence 
the  fold  can  not  extend  farther  in  this  direction.  The  projection  of  the 
trough  of  the  syncline  along  its  pitch,  as  calculated  from  its  known  posi- 
tion on  the  fifth  and  sixth  levels  of  the  mine,  would  bring  it  to  the  surface 
at  just  about  the  west  end  of  these  exposures. 

In  the  discussions  of  the  fohlsof  the  Aragon  mine  no  reference  ha.s 
been  made  to  the  small  folds  imposed  upon  the  larger  ones.  If  the  Aragon 
synclines  are  secondary  folds,  these  smaller  ones  are  tertiary.  Upon  these, 
in  some  places,  folds  of  the  fourth  order  are  known  to  occur,  but  they  have 
not  been  carefully  enough  worked  out  to  warrant  platting.  The  tertiary 
folds  are  well  seen  on  the  sides  of  the  syncline  shown  in  the  plan  of  the 
fifth  level  of  the  mine  (see  fig.  20).  This  is  the  northern  syncline.  On  the 
plats  of  some  of  the  other  levels  tertiary  folds  are  also  indicated,  but 
nowhere  else  are  they  as  strikingly  exhibited  as  on  the  maps  of  the  fifth 
level.  ', 

West  Vulcan  fold. — East  of  the  Aragon  mine  the  southern  margin 
of  the  dolomite  belt  is  covered  by  thick  beds  of  the  Lake  Superior  sand- 
stone, except  at  a  very  few  widely  scattered  points.  Moreover,  the  mining 
operations  have  disclosed  the  dolomite  in  only  a  few  places  within  the 
underground  workings.  Therefore  no  definite  folds  of  the  dolomite  series 
have  been  recognized  in  this  portion  of  the  belt.  There  are,  however, 
abundant  indications  that  such  folds  exist. 


246  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

In  contact  with  the  dolomite  and  south  of  it  is  the  belt  of  the  iron- 
bearing  Vulcan  formation.  In  this  several  folds  have  been  discovered  by 
explorations  for  ore.  In  the  western  portions  of  the  district,  where  both 
the  dolomite  and  the  iron  formation  are  exposed,  the  former  is  seen  to 
behave  like  the  latter.  Where  this  is  folded  the  underlying  dolomite  is 
likewise  folded,  and  the  folds  possess  the  same  character  as  those  of  the 
overlying  rocks.  If  the  two  formations  behave  in  the  same  way  in  the 
eastern  portion  of  the  belt,  and  there  is  no  reason  to  suppose  that  they  do 
not,  there  must  be  several  minor  folds  on  the  margin  of  the  dolomite 
between  the  Arag-on  mine  and  Waucedah.  The  best  defined  of  the  folds 
in  the  iron  formation  has  been  developed  near  the  west  quarter  post  of 
sec.  10,  T.  39  N.,  R.  29  W.,  on  the  surface,  and  in  the  West  Vulcan  mine 
underground  (see  figs.  45-50).  The  plan  of  this  fold  on  the  surface  is 
shown  on  PI.  XXXIV.  Its  axis  pitches  nearly  west  and  its  axial  plane 
probably  dips  nearly  vertically.  The  corresponding  fold  in  the  dolomite 
to  the  north  must  have  approximately  the  same  pitch  and  dip.  It  ig, 
however,  covered  by  the  Cambrian  sandstone,  and  consequently  is  not 
visible.  Its  position  on  the  surface  must  be  somewhere  near  the  center  of 
ihe  section. 

Other  secondary  folds  at  the  southern  margin. — Another  fold  within  the 
iron  formation  has  been  observed  west  of  No.  3  shaft  of  the  East  Vulcan 
mine  in  the  southwest  portion  of  sec.  11,  T.  39  N.,  R.  29  W.  (PI.  XXXV), 
and  within  the  workings  of  this  shaft  and  No.  4  shaft  of  the  same  mine 
farther  east  (figs.  51-53).  This  fold,  however,  is  known  to  exist  only  in 
the  xipper  members  of  the  Vulcan  formation.  Its  presence  in  the  lower 
member  has  not  yet  been  recognized,  and  consequently  it  is  not  certain  that 
the  dolomite  which  is  still  lower  in  the  succession  was  involved  in  the 
folding. 

There  are  no  other  folds  indicated  along  the  southern  margin  of  the 
southern  dolomite  belt,  though  they  may  exist.  The  country  east  of  the 
East  Vulcan  mine  has  not  been  thoroughly  explored,  and  until  explorations 
are  sufficiently  numerous  to  delineate  the  margin  of  the  dolomite  area  with 
a  close  degree  of  accuracy  it  will  be  impossible  to  declare  whether  folds 
exist  in  it  or  not. 

Secondary  folds  at  the  northern  margin. — The  recognition  of  the  existence 
of  secondary  folds  along  the  northern  border  of  the  southern  dolomite  belt 


ALGONKIAN,  RANDVILLE  DOLOMITE.  247 

is  dependent  on  the  distribution  of  the  dolomite  with  respect  to  the  overlying 
rocks.  The  mapping  of  this  distribution  exhibits  the  fact  that  the  dolomite 
contact  in  several  places  is  marked  by  embayments  (see  pp.  205-206),  which 
can  only  be  explained  as  due  to  crumpling  into  synclines  and  anticlines. 
Corroborative  evidence  that  such  crumpling  does  exist  at  some  of  these 
places  is  afforded  by  the  attitude  of  the  dolomite  beds  at  the  apices  of  the 
assumed  folds.  The  most  notable  instances  of  this  kind  of  evidence  are 
found  in  sec.  36,  T.  40  N.,  R.  30  W.,  and  sec.  3,  T.  39  N.,  R.  29  W.  Near 
the  center  of  sec.  35,  just  east  of  the  apex  of  a  supposed  anticline,  a  number 
of  exposures  occur  along  both  sides  of  the  branch  of  the  Chicago  and 
Northwestern  Railway  that  connects  with  the  main  line  east  of  Quinnesec 
(see  PI.  XXXIX).  The  ledges  consist  of  beds  of  quartzose  and  normal 
dolomite,  which  in  places  are  distinctly  schistose.  In  many  instances  the 
schistosity  is  parallel  to  the  bedding,  both  having  a  strike  of  N.  70°  to  85° 
W.,  and  a  dip  of  78°  to  80°  N.  to  70°  S.,  but  in  several  instances  the 
bedding  and  the  schistosity  are  at  variance.  The  latter  is  more  pronounced, 
bvit  close  examination  of  the  ledges  will  always  reveal  the  former.  Often 
the  two  structures  will  be  found  to  coincide,  but  in  many  cases  the 
schistosity  will  be  seen  to  cut  the  bedding  at  varying  angles  up  to  90°. 
North-soiith  strikes  are  sometimes  observed  and  dips  of  35°  to  45°  W. 
The  platting  of  these  indicates  the  existence  of  small  folds  at  these  points 
with  a  pitch  of  30°  to  40°  W.  Thus  is  corroborated  the  view  that  a  fold  of 
greater  magnitude  exists  in  the  dolomite  at  this  place. 

In  the  southeast  quarter  of  sec.  3,  T.  39  N.,  R.  29  W.,  is  a  single  exposure 
of  dolomite,  the  bedding  and  schistosity  of  which  are  not  coincident.  The 
beds  are  much  crumpled  and  the  little  folds  seem  to  have  a  low  pitch  to  the 
west.  The  location  of  the  exposure  is  at  the  apex  of  the  assumed  anticline 
opposite  the  Norway  syncline  in  the  south  side  of  the  belt.  Its  presence 
adds  plausibility  to  the  mapping  of  a  fold  at  this  place. 

In  sec.  11,  T.  39  N.,  R.  29  W.,  the  presence  of  a  marginal  fold  is  also 
indicated  by  the  existence  cJf  slates  within  the  area,  which,  in  the  absence 
of  a  fold,  would  be  occupied  by  dolomite.  This  is  the  only  evidence  of 
the  presence  of  the  fold  in  this  place. 


INTERIOR   FOLDS. 


In  the  interior  of  the  dolomite  areas  indications  of  close  folding  are  but 
rarely  met  with,  and  when  seen  the  folds  are  not  sufficiently  characterized 


248  THE  MENOxVIINEE  mON-BEARING  DISTRICT. 

to  warrant  safe  couclusions  as  to  their  exact  nature.  Moreover,  it  is  only 
in  the  southern  belt  that  they  are  exhibited.  At  several  places  in  the 
interior  of  this  belt  the  dips  and  strikes  over  small  areas  are  in  different 
directions,  thus  showing  the  presence  of  folds  of  some  kind. 

One  of  the  places  at  which  folding  may  be  observed  is  at  the  west 
end  of  the  hill  north  of  the  Chapin  mine.  Here  a  large  ledge  is  exposed 
at  from  670  to  780  paces  west  and  from  560  to  650  paces  north  of  the 
southeast  corner  of  sec.  30,  T.  40  N.,  R.  30  W.  As  a  whole  the  layers 
composing  the  ledge  are  evenly  bedded  with  a  strike  N.  74°  W.,  and  a  dip 
85°  to  87°  N.,  but  some  of  the  beds,  consisting  of  thin  layers  of  dolomite 
and  quartzite,  are  folded  within  themselves  into  numerous  sharp  anticlines 
and  synclines  following  each  other  in  rapid  succession.  The  axes  of  the 
folds  plunge  almost  vertically  to  the  north. 

In  the  large  ledges  north  and  east  of  Quinnesec  folding  is  common 
(see  PI.  XXXIX).  The  beds  in  some  places  are  crossed  by  faults  with 
throws  of  a  few  inches  to  a  few  feet.  In  other  places  the  rock  is  much 
fractured  and  all  traces  of  bedding  have  been  obliterated.  In  the  southeast 
quarter  of  sec.  34,  northeast  of  the  Quinnesec  mine,  distinct  crumplings  are 
noted.  In  a  few  instances  the  beds  strike  nearly  north.  At  one  place  a 
strike  of  N.  25°  W.  was  measured,  but  this  is  maintained  for  only  a  short 
distance.     The  normal  strike  is  N.  70°  to  80°  W. 

In  other  portions  of  the  belt  the  beds  are  for  the  most  part  very 
uniform  in  their  strikes  and  for  a  given  area  also  in  their  dips.  These  are 
for  the  most  part  nearly  vertical,  but  occasionally,  near  the  borders  of  all 
the  belts,  dips  as  low  as  37°  have  been  observed,  and  in  one  case  a  dip  of 
25°  was  measured,  but  in  these  instances  the  low  dips  are  local  phenomena, 
for  the  beds  in  neighboring  ledges  have  high  dips.  These  rapid  local 
variations  in  dips  indicate  close  folding,  but  since  the  strikes  are  main- 
tained with  a  uniform  direction  the  exact  character  of  the  folding  is  not 
discernible. 

THICKNESS. 

At  no  place  within  the  area  mapped  is  the  dolomite  known  to  be  exposed 
from  the  bottom  to  the  top.  On  the  northern  side  of  the  trough  the  forma- 
tion is  bordered  by  the  Sturgeon  quartzite  on  the  north  and  the  Vulcan 
formation  on  the  south,  but  exposures  between  these  limits  are  so  few  that 
we  can  not  be  sure  that  the  dolomite  occupies  the  entire  breadth. 


ALGONKIAN,  KANDVILLE  DOLOMITE.  249 

If,  however,  we  assume  that  in  the  wider  portions  of  the  belt  the  entire 
formation  is  exposed,  we  are  still  unable  to  estimate  its  thickness  accurately, 
since  we  know  that  it  has  been  subjected  to  subordinate  folding-,  and  we  can 
not  determine  the  exact  amount  of  duplication  of  beds  resulting  therefrom. 

It  is  only  in  the  southern  area  that  data  can  be  obtained  for  estimating 
even  approximately  the  thickness  of  the  formation.  The  width  of  the 
exposed  portion  of  this  belt  is  about  4,000  feet,  measured  across  the  strike 
of  the  beds  north  of  the  Quinnesec  mine.  The  dips  vary  from  88°  N. 
to  70°  S.  Assuming  the  dips  to  average  80°  S.,  and  the  formation 
to  be  folded  into  a  simple  anticline,  the  corresjDonding  thickness  would  be 
1,900  feet.  This  estimate  is,  however,  of  little  value,  since,  on  the  one 
hand,  we  can  not  know  what  proportion  that  part  of  the  formation  which  is 
here  exposed  bears  to  the  entire  formation,  nor  can  we,  on  the  other  hand, 
estimate  the  amount  of  thickening  due  to  minor  folding.  That  the  entire 
formation  is  not  exposed  from  bottom  to  top  is  evident  from  the  fact  that 
the  contact  with  the  vmderlying  Sturgeon  quartzite  is  not  seen.  Moreover, 
the  layers  of  chert  that  are  believed  to  be  characteristic  of  the  upper  horizons 
of  the  formation  are  likewise  absent,  probably  as  the  result  of  the  erosion 
that  took  place  between  Lower  and  Upper  Menominee  time.  In  view  of 
these  facts  alone,  the  estimate  given  above  would  seem  to  be  too  small.  But 
minor  folding  must  exist  in  this  area.  The  variations  in  the  strikes  and  dips 
of  the  dolomite  beds  northeast  of  Quinnesec  have  already  been  referred  to 
as  indicative  of  folding.  Moreover,  the  existence  of  a  syncline  in  the  belt  just 
east  of  the  section  under  discussion  (see  pp.  239-240)  has  been  mentioned. 
This  syncline  is  so  near  the  present  section  that  its  influence  must  extend  to 
it,  and  an  apparent  thickening  of  the  formation  must  be  the  result.  How 
great  the  reduplication  of  beds  due  to  these  folds  is  can  not  be  determined, 
bi;t  it  is  clear  that  the  estimate  given  is  higher  than  it  should  be  were  the 
formations  not  affected  by  them.  Whether  the  estimate  would  be  increased 
or  diminished  by  the  elimination  of  the  doubtful  elements  from  the  discus- 
sion is  entirely  unknown. 

In  the  center  of  sec.  12,  T.  39  N.,  R.,  29  W.,  we  find  the  most  contin- 
uous set  of  dolomite  exposures  in  the  district.  Near  the  north-south  quarter 
line  the  belt  is  about  3,000  feet  wide  and  has  an  average  dip  of  55°  S. 
This  corresponds  to  a  breadth  of  approximately  2,450  feet,  which  must  be 
at  least  twice  the  thickness  of  the  formation,  since  this  belt  is  an  anticline. 


250  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

So  far  as  we  can  learn,  there  are  no  minor  folds  here,  so  that  1,225  feet 
must  be  accepted  as  the  greatest  possible  thickness  of  the  formation  exposed 
at  this  place.  The  entire  formation,  however,  does  not  reach  the  suiface, 
for  the  beds  in  the  center  of  the  belt — those  at  the  apex  of  the  anticline,  and 
consequently  the  lowest  members  exposed — are  not  the  basal  members  of 
the  formation.  Moreover,  while  the  southern  limit  of  the  dolomite  is  well 
established  by  exposures  of  the  Vulcan  formation,  it  is  not  known  whether 
the  contact  is  at  the  top  of  the  dolomite  or  whether  some  of  this  rock  had 
been  removed  by  erosion  before  the  deposition  of  the  iron  formation. 
Further,  the  northern  limit  of  the  dolomite  belt  is  not  definitely  known,  for 
north  of  the  exposures  of  this  dolomite  the  country  is  covered  with  swamps 
and  sand  plains. 

An  estimate  of  the  thickness  of  the  formation  based  upon  the  above 
statement  of  facts  would  appear  to  be  too  small,  because  the  lower  and 
higher  beds  of  the  dolomite  are  not  exposed.  However,  superimposed 
upon  the  major  folds,  as  already  pointed  out,  are  many  minor  folds.  To 
what  extent  the  beds  are  duplicated  by  this  minor  folding  it  is  practically 
imposible  to  determine.  The  difficulties  here  are  practically  the  same  as 
were  met  with  in  the  attempt  to  calculate  the  thickness  of  the  formation  in 
the  Quinnesec  section.  Although  the  data  are  more  complete  in  these  two 
sections  than  anywhere  else  in  the  entire  district,  there  is  still  a  great  deal 
to  be  demanded  before  the  calculations  based  upon  them  can  be  accepted 
as  possessing  a  close  degree  of  accuracy.  If  one  should  make  calculations 
so  as  to  obtain  a  minimum  figure,  1,000  feet  or  less  could  be  obtained.  If, 
on  the  other  hand,  one  were  to  make  calculations  on  the  supposition  that 
all  of  the  isoclinal  beds  in  the  sections  are  diff'erent  layers,  an  estimate  as 
great  as  5,000  feet  could  be  obtained.  Probably  the  truth  is  much  nearer 
the  lower  figure  than  the  higher.  The  original  thickness  of  the  dolomite  is 
pi-obably  somewhere  between  1,000  and  1,500  feet. 

RELATIONS  TO  ADJACENT  FORMATIONS. 

Relations  to  underlying  Sturgeon  quartzite. — The  dolomite  formation  is 
nowhere  seen  in  actual  contact  with  the  Sturgeon  quartzite,  nor  are  ledges  of 
the  two  formations  seen  in  close  proximity.  It  is  known,  however,  that  the 
upper  layers  of  the  quartzite  are  calcareous  and  that  the  lower  beds  of  the 
dolomite  are  quartzose.     The  three  dolomite  ledges  nearest  to  the  quartzite 


ALGONKIAN,  RANDVILLE  DOLOMITE.  251 

are  as  follows:  One  in  the  northeast  quarter  of  sec.  33,  T.  40  N.,  R.  29  W.; 
one  on  the  south  bank  of  the  Sturgeon  River,  near  the  center  of  sec.  8, 
T.  39  N.,  R.  28  W.;  and  the  third  in  the  northeast  quarter  of  sec.  3,  T.  40  N., 
R.  30  W.  None  of  these  ledges  are  so  near  the  quartzite  that  they  can  be 
said  to  represent  undoubted  transition  phases  between  the  two  formations. 
They  unquestionably  indicate  the  character  of  the  transition,  however,  for 
all  three  ledges  are  near  the  base  of  the  dolomite  series,  and  all  three  are 
composed  largely  or  exclusively  of  quartzose  dolomites.  The  westernmost 
ledge  has  already  been  described  in  some  detail  (see  p.  193).  That  in  sec. 
33  is  compact  in  the  interior  and  drusy  on  the  surface.  The  easternmost 
ledge  is  friable  and  sand}^  The  inference  seems  to  be  safe  that  the  two 
formations  grade  into  one  another  through  dolomitic  quartzites  or  quartzitic 
dolomites,  and  therefore  that  they  are  conformable. 

Relations  to  overlying  Negaunee  formation. — While  there  is  no  evidence 
that  any  of  the  Negaunee  formation  now  occurs  in  the  Menominee  district, 
there  is  abundant  evidence  that  it  occurred  above  the  dolomite  before 
the  erosion  interval  that  separates  the  Lower  Menominee  and  the  Upper 
Menominee  series.  In  most  places  the  erosion  not  only  removed  the 
Negaunee  formation,  but  it  also  cut  down  into  the  Randville  series,  and 
in  most  places  removed  its  upper  portions.  In  a  few  places  above 
the  normal  dolomite  thei-e  still  remain  beds  of  cherty  quartzite,  some- 
times brecciated,  but  at  other  times  nonbrecciated,  and  distinctly  bedded. 
The  nature  of  the  cherty  quartzite  suggests  the  idea  that  it  may  represent 
a  transition  between  the  dolomite  beneath  it  to  an  iron  formation  that  may 
have  been  immediately  above  it.  In  its  macroscopic,  as  well  as  its  micro- 
scopic character,  the  cherty  rock  resembles  some  phases  of  the  jaspilites 
associated  with  the  ores  of  the  Marquette  district.  The  pebbles  in  the  con- 
glomerates that  prove  the  former  existence  of  the  Negaunee  formation  in 
the  Menominee  district  show  that  the  iron  formation  in  this  district  was 
identical  with  the  corresponding  formation  so  well  developed  in  the  Mar- 
quette district.  While  conclusive  evidence  of  the  fact  is  lacking,  neverthe- 
less it  is  probable  that  the  formation  which  in  this  report  has  been  called 
the  Randville  formation  graded  into  the  now  absent  Negaunee  formation 
through  these  cherts.  It  is  possible  that  had  a  considerable  quantity  of 
the  iron  formation  remained  for  study  the  line  between  this  formation  and 
the  underlying  dolomite  series  would  be  found  more  naturally  to  belong 


252  THE  AIENOMINEE  IRON-BEARING  DISTRICT. 

IjetAveen  the  dolomite  and  the  cherty  quartzite  than  at  the  top  of  the  latter 
rock,  which  would  then  belong  at  the  base  of  the  Negauuee  formation  as 
the  lowest  portion  of  a  jaspilite  member. 

The  relations  of  the  dolomite  with  this  rock  would  thus  become 
siffuiticant.  So  far  as  has  been  observed  in  the  few  cases  where  contacts 
have  been  seen,  the  dolomite  and  the  nonbrecciated  phases  of  the  cherty 
quartzite  are  conformable.  The  contact  between  the  two  is  in  some  cases 
sharp,  a  well-defined  layer  of  chert  resting  directly  upon  dolomite.  In 
other  cases  the  two  rocks  seem  to  grade  by  interlaminations.  This  seems 
to  be  the  condition  just  north  of  the  Norway  pit,  where  near  the  top  of 
the  dolomite  at  this  place  a  few  alterations  of  the  typical  carbonate  with  a 
red  cherty  quartzite  occur,  and  where  occasionally  what  look  like  veins  of 
the  latter  rock  penetrate  the  underlying  rock.  There  are  no  definite 
cherty  beds  of  any  great  thickness  above  the  dolomite  at  this  place,  though 
the  chert  seems  to  be  most  prevalent  in  the  uppermost  of  the  exposed 
hoi'izons. 

The  shattered  and  jointed  character  of  the  autoclastic  breccias  makes 
it  exceedingly  difficult  to  discern  the  true  relations  of  these  phases  of  the 
rock  to  the  dolomite  with  which  they  are  in  contact,  though  there  seems  to 
be  little  doubt  that  they  are  also  conformable  with  the  underlying  rock. 
No  place  has  been  seen  where  the  cherty  breccias  are  in  direct  contact 
with  the  members  of  the  underlying  formation,  except  at  Iron  Hill,  where 
the  cherts  are  associated  with  a  dolomite  conglomerate.  But  at  this  place 
the  relations  are  so  exceedingly  complicated  that  little  can  be  learned  from 
them  (see  p.  256). 

Relations  to  basal  member  of  the  Upper  Huronian. — Contacts  between  the 
dolomite  and  the  overlying  formation  of  the  Upper  Huronian  are  found  in 
many  of  the  mines,  but  they  are  nowhere  discoverable  on  the  surface.  In 
the  little  ravine  just  east  of  the  old  Brier  Hill  mine  the  dolomite  and  the 
lower  members  of  an  iron  formation  are  very  close  together,  but  their  actual 
contact  is  covered.  The  dolomites  and  the  slates  on  either  side  of  the  con- 
tact plane  strike  N.  81°  W.,  and  dip  65°  S.,  and  no  evidence  of  discordance 
between  them  can  be  discovered.  However,  the  space  between  the  ledges 
of  the  two  formations  is  filled  with  loose  fragments,  and  among  these  frag- 
ments are  large  pieces  of  quartzite  holding  pebbles  of  jaspilite,  quartzite, 
granite,  and  other  members  of  the  Archean.     The  presence  of  the  jaspilite 


ALGOMKIAN,  RANDVILLE  DOLOMITE.  253 

fragments  in  the  conglomerate  is  proof  that  beneath  this  rock  layer  there 
existed  somewhere  in  the  Lower  Menominee  series  an  iron  formation  con- 
taining considerable  jasper.  This  formation  has  now  completely  or  almost 
completely  disappeared,  so  far  as  the  surface  indications  show.  It  is 
assumed  that  it  has  been  cut  away  by  erosion,  and  that  its  debris  furnished 
the  jaspilite  fragments  in  the  conglomerate. 

In  the  mines  and  the  open  pits  a  similar  conglomerate  or  a  coarse 
quartzite  is  frequently  found  lying  upon  the  dolomite.  Jaspilite  fragments 
can  not  in  all  places  be  detected  in  it,  but  they  can  be  observed  in  so  many 
localities  that  the  only  acceptable  interpretation  of  the  phenomenon  is  that 
the  dolomite  and  the  quartzite  are  separated  by  an  unconformity.  The 
contact  between  the  two  rocks  is  sharp.  There  is  no  gradation  of  any  kind 
between  them.  The  dolomite  near  the  contact  is  usually  schistose,  so  much 
so  that  in  most  cases  it  is  a  talc-schist.  The  schist  was  probably  formed 
in  connection  with  movement  along  the  contact  plane  after  the  Upper 
Huronian  deposits  were  laid  down  and  contemporaneously  with  the  folding 
and  metamorphism  that  affected  both  tlie  Lower  Menominee  and  Upper 
Menominee  series.  The  contact  between  the  schist  and  the  superjacent 
quartzite  is  extremely  sh^rp,  and  in  many  places  the  plane  of  contact  is 
slickensided. 

In  those  places  where  the  basal  member  of  the  iron  formation  is  not  a 
coarse  quartzite,  it  is  usually  a  bedded  red  slate;  or  more  nearly  a  schist 
composed  of  small  grains  of  quartz  and  considerable  dolomite  and  sometimes 
talc.  Alternate  bands  are  composed  of  layers  in  which  dolomite  and  talc 
are  predominant  and  those  in  which  siliceous  material  predominates.  The 
contacts  between  the  schist  and  the  rocks  on  both  sides  of  it  are  usually 
covered.  At  the  open  pit  of  the  Indiana  mine  this  rock  is  represented  by  a 
fine-grained  pink  and  gray  slate  that  lies  between  the  dolomite  to  the  north 
and  the  iron  formation  to  the  south.  The  rock  may  be  seen  in  the  north 
wall  of  the  pit,  but  its  contact  with  the  dolomite  is  covered.  Drill  holes  in 
the  vicinity  of  the  mine  which  encountered  the  slate  passed  through  about 
25  feet  of  it  directly  into  the  dolomite.  In  the  records  this  slate  is  spoken 
of  as  a  "broken  slate"  formation,  by  which  it  is  inferred  that  the  rock  is 
either  brecciated  or  conglomeratic.  If  the  latter,  it  is  confirmatory  evidence 
of  an  unconformity  between  the  dolomite  and  the  bottom  of  the  iron 
formation. 


254  THE   MENOMINEE  IRON  BEARING  DISTRICT. 

At  the  Norway  open  pit  and  in  the  pits  in  the  northeast  quarter  sec.  9, 
T.  39  N.,  R.  29  W.,  the  original  relations  existing  between  the  dolomite  and 
the  overlj'ing  iron  formation  have  been  greatly  obscured  by  deformations 
due  to  movement.  The  overlying  iron  formation  is  a  coarse  schistose 
conglomerate  or  breccia  composed  of  fragments  of  dolomite,  slates,  and  ore, 
in  a  matrix  composed  of  the  same  substances  subsequently  enriched  by  the 
deposition  of  ferruginous  material.  Many  of  the  fragments  are  angular, 
others  are  rounded.  In  some  instances  the  brecciated  bands  may  be  seen 
to  cut  diagonally  across  unbrecciated  layers  of  the  same  composition, 
indicating  that  the  former  is  autoclastic  in  origin  (see  PI.  XXI,  B).  The 
more  conglomeratic  phases  are  usually  richer  in  dolomitic  fragments  than 
are  the  brecciated  phases.  Their  material  is  more  varied  in  character  and 
their  inclosed  fragments  more  pebble-like.  In  all  its  aspects  the  rock  much 
resembles  a  sedimentary  conglomerate.  But  it  is  also  brecciated.  Large- 
sized  angular  fragments  of  the  rock  are  here  and  there  scattered  through  a 
conglomeratic  matrix  of  the  same  composition  as  the  fragments. 

The  rock  underlying  these  brecciated  ones  is  either  a  talcose  schist,  or 
slate,  or  a  quartzose  dolomite.  In  each  case  this  rock  also  is  brecciated, 
the  included  fragments  and  the  inclosing  matrix  being  of  the  same  com- 
position. There  is  in  some  localities  a  gradation  between  these  underlying 
rocks  and  the  rocks  lying  above  them,  while  in  other  places  the  line  of 
division  between  them  is  well  defined.  Often  there  has  been  extensive 
movement  along  this  crushed  zone,  as  indicated  by  the  schistosity  of  both 
breccias.  This  has  resulted  in  a  very  irregular  contact  between  the  two, 
causing  the  relations  between  them  to  be  so  obscure  that  they  are 
difficult  to  decipher.  The  only  probable  explanation  of  the  facts  observed 
seems  to  be  that  the  conglomeratic  rock  is  a  true  conglomerate  which  was 
deposited  on  the  eroded  surface  of  the  dolomite  and  then,  together  with 
the  underlying  rock,  was  brecciated  and  rendered  schistose  by  the  accom- 
modation movements  along  the  contact  plane  that  took  place  when  the 
district  was  folded.  If  this  view  is  correct,  the  presence  of  the  conglom- 
erate above  the  dolomite  is  further  evidence  of  an  unconformity  between 
the  dolomite  series  and  the  overlying  iron  formation. 

Relations  to  other  formations. — The  relations  existing  between  the 
dolomite  and  the  contiguous  formations  younger  tiian  the  base  of  the  iron 
formation  will  be  discussed  in  connection  with  the  descriptions  of  these 
formations  (pp.  361  and  366). 


ALGONKIAN,  RANDVILLE  DOLOMITE.  255 

INTERESTING  LOCALITIES. 

Although  the  dolomite  series  is  for  the  most  part  covered  by  the  Lake 
Superior  sandstone,  there  are  many  places  where  excellent  exposures  can 
be  studied.  These  are  mainly  in  the  area  of  the  southern  belt  and  gener- 
ally near  the  transverse  gaps  that  have  been  described  as  crossing  the  belt 
at  several  places,  or  on  the  southern  slope  of  the  ridge  of  hills  north  of  the 
line  of  the  most  important  mines.  Though  no  continuous  section  across 
the  entire  formation  has  been  seen,  nevertheless  it  is  thought  that  practi- 
cally all  of  its  beds  from  bottom  to  top  are  exposed  at  different  places. 

IN    THE    NORTHERN   BELT. 

Northeast  quarter  of  sec.  3,  T.  40  N.,  R.  30  W. — The  only  exposures  of 
the  northern  belt  that  are  at  all  extensive  are  those  in  the  northeast  quarter 
of  sec.  3,  T.  40  N.,  R.  30  W.,  and  those  in  the  northeast  quarter  of  sec.  14 
in  the  same  town.  The  former  have  already  been  described  in  connection 
with  the  description  of  the  near-by  exposures  of  Sturgeon  quartzites 
(see  p.  193). 

Northeast  quarter  of  sec.  14,  T.  40  N.,  JR.  30  W. — Near  the  north  quarter 
post  of  sec.  14,  T.  40  N.,  R.  30  W.,  four  distinct  ledges  outcrop  on  the 
south  slope  of  the  valley  of  the  stream  that  empties  into  Pine  Creek  at 
Hamilton  and  Merryman's  camp  No.  6.  They  occur  along  a  line  trending 
about  southwest,  and,  taken  together,  they  exhibit  a  cross  section  of  the 
formation  about  800  feet  in  length.  The  northernmost  ledge,  which  is 
on  the  north  line  of  the  section,  250  paces  east  of  the  quarter  post,  is  a 
massive,  white,  crystalline,  dolomitic  marble  without  noticeable  strike  or 
dip.  About  75  paces  east  and  the  same  distance  southwest  are  two  other 
ledges  in  which  the  rock  is  a  dolomitic  quartzite,  likewise  without  distinct 
strike  or  dip.  The  southernmost  ledge,  about  100  paces  east  and  225  paces 
south  of  the  quarter  post  is  a  fine-grained,  nearly  pure  white  quai'tz  rock 
that  strikes  N.  75°  W.  and  dips  75°  N.  It  is  indistinctly  marked  by  pink 
and  light-gray  bands  that  apparently  indicate  bedding,  and  is  traversed 
by  a  great  profusion  of  quartz  veins.  In  some  places  it  is  cellular  or  drusy. 
On  a  fresh  fracture  the  luster  is  dull  and  resinous  and  quite  unlike  the 
vitreous  luster  of  the  Sturgeon  quartzites.  The  rock  is  a  fairly  good  type 
of  the  cherty  quartz  rocks  occurring  at  the  top  of  the  Randville  formation. 
The  exposure  is  interesting  as  indicating  the  near  proximity  of  the  upper 
boundary  of  the  dolomite  formation. 


256  THE  MENOMINEE  IRON-BEARING  DISTRICT. 


IN    THE    CENTRAL   BELT. 


In  the  area  of  the  central  belt  the  only  exposures  of  note  are  those  just 
west  of  the  Cuff  mine,  in  the  southwest  quarter  of  sec.  22,  T.  40  N.,  R.  30 
W.,  and  those  at  Iron  Hill,  in  sec.  32,  T.  40  N.,  R.  29  W. 

Southwest  quarter  of  sec.  22,  T.  40  N.,  R.  30  W. — In  the  southern  portion 
of  the  southwest  quarter  of  sec.  22,  T.  40  N.,  R.  29  W.,  and  the  neighboring 
portion  of  sec.  21  are  six  isolated  little  knobs  of  typical  dolomite,  forming 
together  a  ridge  of  ledges  extending  for  about  half  a  mile  along  the  north 
side  of  the  road  from  Lake  Antoine  to  the  Cuff  mine.  Some  of  the  ledges 
are  in  sight  of  the  road.  These  appear  as  rough  knobs  partially  covered 
with  trees  and  bushes.  Others  are  buried  in  scrubby  second  growtli  and 
are  in^asible  from  short  distances.  The  exposures  ai'e  interesting  mainly 
as  illustrative  of  the  massive  character  of  much  of  the  dolomite  and  as 
evidence  of  the  existence  of  the  Randville  formation  between  the  Cuff 
mine  and  the  Indiana  mine.  The  rock  in  the  ledges  is  a  massive  pink  or 
gray  dolomite,  heavily  bedded,  with  indistinct  bedding  structure  striking 
about  N.  70°  to  80°  W.  and  dipping  vertically.  The  exposures  are  trav- 
ersed by  gaping  cracks  or  hollows  where  weathering  has  opened  up  the 
bedding  planes,  and  by  cross  gashes  ojiened  up  along  joint  cracks.  Their 
surfaces  are  therefore  rough  and  rugged,  with  projecting  portions  separated 
by  hollows. 

Iron  Hill. — The  central  belt  of  dolomite  terminates  on  the  surface  in 
the  southeast  quarter  of  sec.  32,  T.  40  N.,  R.  29  W.,  where  dolomites,  chei'ts, 
breccias,  and  conglomerates  occur  in  such  relations  as  to  suggest  the  pres- 
ence of  an  eastward-pitching  anticline  with  superimposed  minor  folds.  The 
exposures  at  this  place  have  already  been  referred  to  several  times  on 
preceding  pages  (pp.  219-220,  and  234  and  PI.  XVI,  B,  PI.  XVII,  A,  and 
PI.  XLII).  They  are  easily  reached  from  Norway  by  the  road  running 
north  around  the  east  end  of  the  Norway  open  pit. 

The  ledges  constitute  a  little  plateau  overlooking  a  swamp  to  the  south 
and  southeast.  The  southern  limit  of  this  plateau  is  a  steep  slope  broken 
at  four  places  by  projecting  buttresses  of  rock  with  precipitous  fronts 
ranging  from  15  to  20  feet  high.  On  the  top  of  the  plateau  the  exposures 
are  all  of  one  kind  except  at  the  e'astern  end.  Together  they  form  practi- 
cally a  continuous  ledge  about  a  quarter  of  a  mile  long  and  from  200  feet 
to  500  feet  wide,  extending  in  a  dii-ection  N.  60°  W.     The  main  portion 


ALGONKIAN.  RANDVILLE  DOLOMITE.  257 

of  the  ledges  is  a  well-bedded,  light-gray  or  dark-gray  dolomite  dipping 
nearly  vertically  and  striking  N.  50°  to  60°  W.  Interbedded  with  this  are 
a  few  thin  layers  of  a  very  schistose  qnartzose  dolomite.  North  and  west 
of  the  ledges  the  ground  rises  toward  a  low  hill  underlain  by  the  Lake 
Superior  sandstone  with  a  basal  layer  of  conglomerate,  which  can  be  well 
seen  at  several  places  on  the  east  of  the  dolomite  along  the  eastern  slope  of 
the  plateau  and  in  the  valley  at  its  eastern  base.  On  the  slope  the  sand- 
stone conglomerate  occurs  as  patches  lying  upon  a  cherty  quartz  rock  and 
a  chert  breccia  in  such  a  way  as  to  permit  of  no  doubt  that  it  is  unconform- 
ably  above  them.  -Although  this  rock  in  many  places  consists  largely 
of  cherty  and  dolomitic  fragments  in  a  cherty  and  dolomitic  matrix,  it 
nevertheless  grades  upward  into  a  horizontally  bedded  rock  with  the 
characteristics  of  the  normal  Cambrian  sand  rock.  The  rocks  beneath  this 
conglomerate,  while  in  many  places  possessing  the  same  general  appearance 
as  the  latter,  are  a  little  more  compact.  They  moreover  show  abundant 
evidences  of  folding  and  are  cut  by  joint  cracks  and  penetrated  by  quartz 
veins,  both  of  which  features  are  lacking  from  the  sandstone  conglomerate. 
Farther  up  on  the  slope  cherts  are  well  exposed  in  a  number  of  small  ledges. 
In  some  ledges  the  rock  is  a  fine-grained,  pink,  homogeneous  quartzite 
indistinctly  bedded  and  folded  into  definite  folds.  Most  of  the  ledges, 
however,  especially  those  to  the  soiith,  consist  of  a  cherty  breccia  composed 
of  sharp-edged  fragments  of  a  white  chert  lying  in  a  pink  or  red  matrix 
composed  of  small  grains  of  the  same  white  chert  in  an  extremely  fine- 
grained siliceous  groundmass  that  looks  not  unlike  a  red  felsite.  This  chert 
breccia  may  be  seen  in  places  to  lie  upon  the  dolomite.  It  also  occurs  as 
patches  plastering  the  faces  of  the  little  cliffs  overlooking  the  swamp  to  the 
south  and  as  layers  a  foot  or  two  thick  coating  these  cliffs  and  bending  up  over 
them  (see  PI.  XVII,  A).  The  main  rock  in  the  cliffs  is  a  dolomite  conglom- 
erate which  differs  from  the  chert  breccia  in  the  nature  of  its  pebbles  and 
also  in  the  character  of  its  groundmass.  The  rock  is  dark  gray  in  color 
when  viewed  in  the  ledge.  Its  matrix  is  an  almost  black  cherty  dolomite 
with  intermingled  quartz  grains,  cut  by  tiny  veins  of  calcite  and  quartz.  In 
this  ai'e  numerous  pebbles  of  all  shapes  and  sizes,  the  largest  20  inches  in 
diameter.  The  majority  are  elongated  and  lie  with  their  larger  dunensions 
in  approximately  the  same  direction,  though  variations  from  this  position 
are  very  numerous.  Most  of  them  consist  of  dolomites ;  the  remaining  ones 
MON  XLVI — 0-4 17 


258  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

are  mainly  wliite  chert,  tliougli  a  very  few  consist  of  quartz  or  quartzlte. 
Many  of  the  dolomite  pebbles  still  retain  their  bedding  lines,  and  these  run 
in  all  directions  across  the  pebbles  in-espective  of  their  elongation,  though 
naturallv,  in  the  greater  number  of  cases,  the  bedding  and  elongation  are 
parallel.  Both  pebbles  and  matrix  alike  are  traversed  by  many  fractures 
that  have  been  cemented  by  quartz,  forming  veins  which  now  stand  up  as 
tiny  projecting  ridges  intersecting  one  another  diagonally.  Some  of  these 
may  be  seen  in  PI.  XYI,  B.  The  main  fractm'e  lines  intersect  one  another 
at  angles  of  40°  and  1-40°,  the  acute  angles  opening  in  a  direction  a  little 
to  the  east  of  north,  about  20^,  and  to  the  west  of  south,  and  the  obtuse 
ones  nearly  east  and  west.  Since  the  beds  are  probably  folded  and  the 
apex  of  the  folds  strike  about  N.  60°  W.,  and  pitch  steeply  to  the  east,  the 
direction  of  the  joints  and  their  angular  relations  correspond  \erj  closely 
to  the  directions  which  they  should  have  according  to  the  discussions  of 
Van  Hise."  On  the  horizontal  surfaces  of  some  ledges  a  third  set  of  joints 
may  be  observed  that  appear  as  a  series  of  fine  parallel  cracks  nearly 
bisecting  the  obtuse  ang-les  of  the  two  main  sets.  This  series  in  direction 
nearly  coincides  with  the  strike  of  the  beds  as  observed  in  other  ledges. 
Along  the  main  joint  cracks  minor  displacements  have  often  taken  place 
and  the  rock  within  a  small  fraction  of  an  inch  on  both  sides  of  the  fractui'es 
has  been  sheared.  Moreover,  many  of  the  pebbles  are  mashed  and  faulted, 
thus  showiug  that  the  district  was  deformed  after  the  conglomerate  was  laid 
down. 

In  the  ledges  forming  the  clifts  the  conglomerate  appears  to  ovei'lie  the 
chert  breccia  in  some  places,  but  in  others  the  reverse  condition  obtains. 
In  the  eastei'n  ledges,  as  has  been  stated,  the  breccia  is  usually  above  the 
bedded  dolomite.  In  one  of  these  ledges,  however,  the  chert  breccia  is 
interbanded  with  beds  of  massive  dolomite.  Although  the  breccia  in  the 
eastern  ledges  and  the  conglomerate  in  the  southern  and  western  ledges 
appear  to  be  very  ditferent  rocks,  if  one  begins  at  the  east  and  traces  care- 
fully the  breccia,  step  by  step,  in  the  successive  ledges,  he  must  be  struck 
with  the  fact  that  the  bi'eccia  fragments  become  more  and  more  rounded  as 
he  proceeds  westward,  and  the  rock  assumes  more  and  more  the  character 
of  a  conglomerate,  until  finally  the  typical  conglomerate  is  reached.     No 

"Principles  of  North  American  pre-Cambriau  geology:  Sixteenth  Ann.  Kept.  V.  S.  Geol.  Survey, 
pt.  1,  1894,  pp.  651-654  and  671-672. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  259 

line  of  demarcation  between  the  two  rocks  can  be  detected,  but  the  one 
seems  to  grade  imperceptibly  into  the  other.  This  observation  suggests 
the  possibility  that  the  conglomerate  is  an  autoclastic  rock  and  that  its 
conglomeratic  character  is  due  to  the  easy  attrition  of  the  dolomite  pebbles 
as  compared  with  the  difficult  attrition  of  the  chert  fragments  in  the  breccia. 
At  one  place  toward  the  east  end  of  the  hill  a  conglomerate  band  is  between 
solid  ledges  of  dolomite,  and  is  in  such  a  position  as  to  indicate  that  it  cuts 
diagonally  across  the  bedding  of  the  nonconglomeratic  rock. 

These  relations  between  the  dolomite,  the  chert  breccia,  and  the  con- 
glomerate are  exceedingly  complicated.  The  attempt  to  interpret  them 
leads  to  one  or  the  other  of  the  following  conclusions  :  (1)  The  conglomerate 
may  be  a  true  sedimentary  intraformational  conglomerate  whose  complex 
relations  to  the  remainder  of  the  Randville  dolomite  are  due  to  the  crushino- 
and  close  folding  to  which  the  series  at  this  place  has  been  subjected;  (2)  the 
conglomerate,  like  the  bi'eccia,  may  be  an  autoclastic  rock  formed  by  crushing 
and  abrasion  of  the  autoclastic  fragments  which  in  the  case  of  the  breccia, 
because  of  their  hardness,  retained  their  sharp-edged  forms;  or  (3)  it  may  be 
a  true  conglomerate  at  the  base  of  the  Hanbury  slate,  made  to  appear  like 
an  intraformational  conglomerate  by  repeated  close  folding  at  the  end  of  the 
eastward-pitching  anticline  which  terminates  the  dolomite  belt.  Since 
several  minor  folds  are  superimposed  on  the  anticline  the  conglomerate  would 
naturally  be  folded  in  between  the  underlying  dolomite,  and  upon  erosion 
would  appear  as  an  intraformational  conglomerate.  In  this  case  the  chert 
breccia  would  have  to  be  considered  a  sedimentary  rock.  The  difference 
in  the  character  between  it  and  the  conglomerate  might  be  due  to  the  fact 
that  the  former  was  deposited  against  a  shore  composed  of  chert  and  the 
latter  against  a  dolomite  shore  line  from  which  the  overlying  chert  had  been 
removed  by  erosion.  The  Hanbury  slate — an  Upper  Hui'onian  formation — 
borders  the  dolomite  to  the  south  and  the  east,  though  its  contact  with  the 
dolomite  is  not  visible.  The  normal  Hanbury  slate  is  a  typical  gray 
argillaceous  rock  quite  different  in  composition  from  the  conglomerate  and 
breccia,  but  this  difference  is  easily  explained  by  the  latter  rocks  being  the 
first  deposits  along  a  shore  line  composed  of  dolomite  and  chert. 

While  the  third  view  is  the  one  that  seems  most  satisfactory  to  explain 
the  phenomena,  nevertheless  there  are  a  few  facts  that  are  not  explained 
by  it.     The  presence  of  a  band  of  conglomerate  cutting  diagonally  across 


260  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

several  dolomite  beds  is  explained  best  by  the  second  view.  If  the  breccia 
and  the  conglomerate  do  not  actually  grade  into  one  another  as  they  have 
been  described  to  do,  it  is  possible  that  the  breccia  is  an  autoclastic  rock 
and  the  conglomerate  the  basal  member  of  the  Hanbury  series.  The  inabil- 
ity to  distinguish  a  line  of  demarcation  between  them  may  well  be  due  to 
exceedingly  close  folding  and  a  welding  together  of  the  two  rocks  where 
they  are  in  contact.  No  unprejudiced  observer,  however,  after  reviewing 
the  facts  impartially,  would  be  willing  to  declare  without  reservation  that 
the  conglomerate  is  not  a  member  of  the  dolomite  formation;  nevertheless, 
after  repeated  visits  to  the  ledges  and  careful  examination  of  them,  it  seems 
most  plausible  to  regard  the  conglomerate  as  the  basal  member  of  the  Han- 
bury formation  and  the  breccia  as  an  autoclastic  rock  formed  from  the  upper- 
most (cherty)  members  of  the  dolomite  formation  by  the  fracturing  that 
accompanied  close  folding.  That  the  whole  series  of  deposits  in  this  place 
was  indeed  fractured  is  shown  by  the  numerous  quartz  veins  that  traverse 
them,  but  since  these  veins  cut  indifferently  all  the  rocks,  the  conglomerate 
as  well  as  the  massive  dolomites,  and  the  pebbles  in  the  conglomerate  a§ 
well  as  its  matrix,  this  fracturing  must  have  taken  place  after  the  conglom- 
erates were  laid  down.  It  is  conceivable,  of  course,  that  before  the  con- 
glomerate was  made,  an  earlier  fracturing  took  place  and  that  its  effects 
are  ^^I'eserved  in  the  breccias. 

IN   THE    SOUTHERN   BELT. 

In  the  southern  belt  of  dolomite  the  opportunities  for  the  study  of  the 
formation  are  exceptionally  good.  ExjDOsures  are  fairly  abundant,  and, 
though  limited  very  largely  to  the  sovitli  side  of  the  belt,  they  exhibit  the 
character  of  the  formation  in  all  its  phases.  Some  of  the  most  interesting 
groups  of  exposures  are  those  discussed  in  the  following  paragraphs. 
There  are  many  others  in  addition  to  those  described  that  are  worth  study, 
but  these  represent  all  the  phases  of  the  formation,  and,  besides,  they  are 
easily  accessible. 

Southeast  side  of  Lake  Antoine. — The  ledges  on  the  southeast  side  of 
Lake  Antoine  are  best  reached  by  the  road  from  Iron  Mountain  that  passes 
along  the  south  side  of  the  lake.  They  form  a  little  hillock  on  the  east  and 
south  sides  of  the  road  almost  due  east  of  the  little  island  in  the  southern 
portion  of  the  lake. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  261 

The  rocks  outcropping  on  the  top  and  along-  the  south  slope  of  this 
hillock  are  well-bedded  dolomites  and  dolomitic  quartzites,  the  latter  often 
exhibiting  cross  bedding-.  The  surfaces  of  the  ledges  are  roughly  corru- 
gated. The  dolomite,  weathering  more  rapidly  than  the  quartzite,  forms 
the  hollows  of  the  corrugations,  while  the  quartzite  forms  the  ridges.  All 
the  beds  dip  vertically  and  strike  N.  71°  to  75°  W.  The  predominant 
dolomite  is  a  bluish-gray  rock,  containing  here  and  there  a  grain  of  quartz. 
It  is  cut  by  small  veins  of  quartz,  and  others  of  a  mixture  of  quartz  and 
dolomite.  On  a  fresh  fracture  surface  the  rock  is  tine  grained,  hon:io- 
geneous,  and  entirely  massive.  On  the  light-brown  weathered  surface, 
however,  many  very  distinct  oval  grains  of  quartz  are  apparent,  scattered 
indiscriminately  through  the  rock  in  particles  measuring  a  millimeter  in 
their  longest  diameters,  which  are  nearly  always  in  the  plane  of  the  rock's 
bedding.  Moreover,  the  rock  appears  distinctly  schistose  through  the 
presence  of  a  great  number  of  ver}"  thin  seams  of  argillaceous  dolomite, 
which  run  parallel  to  the  bedding  for  short  distances  and  then  disappear, 
their  places  being  taken  by  other  seams  starting  near  the  terminations  of 
the  first  ones  and  disappearing  in  turn  a  centimeter  or  so  beyond  their 
starting  points.  The  effect  of  these  seams,  which  are  approximately  paral- 
lel, but  which  sometimes  make  very  acute  angles  with  one  another,  is  to 
break  the  surface  up  into  a  number  of  elongated  areas,  some  of  which  are 
flat  rhombs,  thus  producing-  an  appearance  of  schistosity.  There  is  no 
evidence  of  shearing  in  the  dolomite.  The  phenomenon  just  described  is 
probably  a  direct  result  of  sedimentation. 

Interbedded  with  the  gray  dolomite  is  a  lighter-colored  one  of  a 
pinkish-gray  tint,  that  differs  from  the  gray  variety  only  in  color  and  in 
the  presence  of  a  few  more  quartz  grains.  The  dolomitic  quartzite  is 
evidently  only  a  very  quartzose  phase  of  the  dolomite.  It  forms  beds  from 
1  inch  to  2  feet  in  thickness  between  beds  of  the  dolomite.  Often  these  ai'e 
so  very  quartzose  that  the  rock  weathers  with  a  surface  almost  identical 
with  that  of  the  Sturgeon  quartzite.  These  ledges  are  interesting  as 
exhibiting  the  best  illustration  of  the  interlaminations  of  dolomitic  and 
quai'tzose  beds  observed  in  the  district. 

Southeast  quarter  of  sec.  32  and  southwest  quarter  of  sec.  33,  T.  40  N., 
B.  30  W. — The  upper  cherty  members  of  the  dolomite  series  are  well 
shown  in  the  large  ledges  occurring  in  the  southeast  quarter  of  sec.  32,  and 


262  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

the  southwest  quarter  of  sec.  33,  T.  40  N.,  R.  30  W.,  south  and  southwest 
of  the  Pewabic  ore  pit  near  the  east  quarter  post  of  sec.  32  (Pis.  XXIX 
and  XXXVIII). 

Through  this  area  a  number  of  hillocks  of  dolomite  occur,  forming  a 
little  plateau  whose  south  escarpment  consists  of  little  cliffs  faced  with  a 
porous,  mottled  red  and  white,  drusj^  and  saccliaroidal  quartz  rock,  crossed 
by  numerous  narrow  streaks  of  a  darker  red  color  and  gashed  by  short, 
irregular  crevices.     No  bedding  can  be  discovered  in  the  quartz  rock,  but 
on  the  plateau  a  little  back  from  the  edge  of  the  cliff  dolomite  occurs  with 
a  well-defined  strike  N.  66°  W.,  and  an  almost  vertical  dip.     The  narrow 
dark-red  streaks  that  traverse  the  quartz  rock  run  in  approximately  parallel 
directions.     They   seem  to  be  tiny  veins  of    quartz  that  occupy  crevices 
parallel  to  the  bedding  planes.     In  places  the  cracks  which  they  occupy 
widen    out    and  hollows    are    fqrmed,   the    walls   of    which   are   covered 
with    druses  of    tiny  quartz    crj-stals.     Often    the    veins  anastomose,  cut 
across    the  portions  of  the  rock  included  between  two  parallel  veins,  and 
separate  it  into  isolated  portions  that  look  like  fragments  derived  from  a 
preexisting  rock.     Near  the  top  of  the  cliff  the  vein  material  predominates 
over  the  fragments,  causing  the  rock  to  resemble  a  typical  breccia  composed 
of  sharp-edged  white  chert  and  iiue-graiued  quartzite  fragments  in  a  dark- 
red  quartzite  matrix.     In  other  places,  probably  where  movement  within 
the  rock  mass  has  separated  fragments,  crushed  some  and  caused  others  to 
assume  new  positions,  quite   different  from   their  original  ones,  the  rock 
resembles  a  basal  breccia  or  conglomerate  of  the  Lake  Superior  sandstone, 
from  which  it  can  be  distinguished  only  hj  the  coarser  grain  of  the  latter 
rock  and  the  greater  drusiness  of  the  former.     At  the  top  of  the  cliff  and  a 
httle  back  from  its  face  the  two  rocks  are  in  contact,  the  sandstone  breccia 
overlying  the  cherty  quartz  breccia.     Even  when  so  near  together,  it  is  not 
always  possible  to  discriminate  between  the  two.     From  the  base  of  the 
sandstone  breccia  veins  and  dikes  of  sandstone  extend  down  for  some  little 
distance  into  the  cherty  rock.     Back  from  the  edge  of  the  cliff,  for  a  width 
of  100  paces  or  more,  the  dolomite  is  well  exposed  in  an  almost  continuous 
ledge  of  a  pink  and  gray  fine-grained  massive  rock,  cut  by  the  usual  quartz 
veins.     The  dips  and  strikes  vary  somewhat  in  different  portions  of  the 
ledge,  but  the  general  strike  is  N.  66°  W.  for  the  southern  portion  of  the 
exposure  and  N.  80°  W.  for  the  northern  part.     The  dip  remains  nearly 
constant.    Where  good  observation  can  be  made  it  is  about  85°  to  87°  S. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  263 

Farther  east  the  dolomite  is  exposed  in  a  number  of  smaller  ledges 
that  rise  above  the  general  surface  of  the  country  in  little  hillocks.  Here 
the  strike  bends  a  little  farther  to  the  west  and  the  dip  in  some  places  is 
as  low  as  37°  S.  The  tops  of  the  hillocks  in  several  instances,  both  in 
sees.  32  and  33,  are  covered  with  remnants  of  the  basal  Lake  Superior 
conglomerate,  which  to  the  north  is  replaced  by  the  usual  sandstone  that 
nearly  everywhere  caps  the  high  ridge  lying  north  of  the  belt  of  mines 
along  the  main  line  of  the  railroad.  This  conglomerate,  or,  in  some  places, 
more  properly  breccia,  is  made  up  of  many  angular  fragments  of  quartzite 
in  a  red  sandy  matrix,  which  in  some  instances  is  highly  calcareous.  At 
the  Pewabic  pit  it  consists  of  many  bowlders  of  a  high-grade  iron  ore 
embedded  in  a  sandstone  matrix  which  differs  from  the  ordinary  sandstone 
simply  in  being  admixed  with  considerable  finely  comminuted  ore.  At 
several  places  within  and  near  the  pit  the  conglomerate  can  be  seen  resting 
unconformably  upon  the  underlying  dolomite,  with  its  horizontal  beds  cap- 
ping the  upturned  beds  of  the  dolomite  and  filling  all  the  many  irregularities 
of  its  surface. 

North  and  northeast  of  Quinnesec. — Another  interesting  group  of 
exposures  is  in  sees.  2  and  3,  T.  39  N.,  R.  30  W.,  and  sees.  34  and  35,  T.  40 
N.,  R.  30  W.,  north  and  northeast  of  Quinnesec.  The  most  instructing  ledges 
are  easily  reached  from  the  wagon  road  between  Quinnesec  and  Norway 
and  from  the  branch  of  the  Chicago  and  Northwestern  Railway  running 
through  sees.  2  and  35.  These  exposures  have  already  been  referred  to 
several  times  in  previous  pages  (see  pp.  239-240,  and  PI.  XV,  A  and  B, 
and  PI.  XXXIX). 

Just  north  of  the  Norway  wagon  road,  east  of  Quinnesec  and  parallel 
to  it,  an  almost  bare  ledge  extends  for  a  quarter  of  a  mile,  forming  a  series 
of  rough  knobs  with  nearly  precipitous  south  sides  (see  PI.  XV,  A 
and  B).  The  rock  of  these  knobs  is  a  heavily  bedded  light-gray, 
fine-grained,  and  usually  massive  dolomite,  striking  N.  70°  W.  and  dipping 
70°  to  80°  S.  It  is  banded  with  the  usual  quartzose  dolomite  layers,  and 
is  cut  by  small  irregular  quartz  veins. 

To  the  north  and  northwest  of  this  are  other  ledges  of  smaller 
dimensions  in  which  the  rock  is  similar.  The  strike,  however,  is  more 
nearly  east  and  west,  and  the  dip  is  much  higher,  sometimes  being  vertical 
or  even  slightly  inclined  to  the  nortji.     The  color  of  the  rock  also  changes 


264  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

to  dark  gray,  pink,  or  red.  Here  and  there  the  beds  show  strong  evidence 
of  compression  in  the  existence  of  a  well-marked  schistosity.  Usually  the 
schistosity  escapes  detection  because  it  is  parallel  to  the  bedding,  but  in  the 
ledge  200  paces  north,  25  to  150  paces  east  of  the  southwest  corner  of  sec. 
35  the  schistosity  is  inclined  to  the  bedding  at  15°,  so  that  the  two  structures 
are  easily  differentiated.  The  strike  of  the  bedding  in  this  ledge  is  N. 
70°  W.  and  that  of  the  schistosity  is  N.  55°  W. 

In  the  southeast  quarter  of  sec.  34  there  are  also  ledges  in  which  the 
strike  of  the  bedding  and  the  schistosity  depart  even  more  from  parallelism. 
In  all  these  instances  it  is  usually  the  bedding  that  is  disturbed,  the 
schistosity  striking  nearly  uniformly  in  a  direction  N.  55°  to  70°  W.,  while 
the  strike  of  the  bedding  varies  between  this  direction  and  due  north.  Here, 
too,  and  in  the  neighboring  portion  of  sec.  35,  there  are  many  exposures  in 
which  minor  faulting  of  a  few  inches  to  a  few  feet  is  noticeable  and  some 
ledsres  in  which  the  dolomite  is  much  fractured  and  all  traces  of  its  origrinal 
bedding  are  lost.  These  disturbances  are  plainly  connected  with  the  great 
fold  at  Quinnesec  (see  p.  239),  since  in  other  portions  of  the  district  at  a 
distance  from  known  folds  disturbances  of  this  kind  are  lacking. 

The  exposures  along  the  branch  railroad  exhibit  one  of  the  best  sec- 
tions across  the  formation  anywhere  met  with  in  the  district.  In  length  it 
measures  a  little  over  three-quarters  of  a  mile.  If  the  view  with  respect  to 
the  structure  advanced  in  previous  pages  (see  p.  239)  is  correct,  the  sec- 
tion cuts  a  broad  anticline  to  the  south,  a  narrower  one  to  the  north,  and  a 
narrow  syncline  between  these.  The  rocks  of  the  southern  half  of  the 
sovithern  syncline  are  described  in  the  preceding  paragraphs.  Those  of  the 
remainder  of  the  section  are  somewhat  different  from  these,  and  are  described 
in  the  following  paragraphs.  The  difference  is  probably  due  to  the  fact 
that  the  northern  portion  of  the  section  is  through  the  upper  portions  of 
the  formation  while  its  southern  part  is  across  lower  portions,  the  upper 
members  having  been  removed  by  erosion  during  inter-Huronian  time. 

The  exposures  along  the  railroad  embrace  a  dozen  or  more  ledges, 
some  small  and  some  large,  lying  on  both  sides  of  the  right  of  way.  Those 
in  sec.  2  and  in  the  southeast  quarter  of  the  southwest  quarter  of  sec.  35  are 
mainly  even-bedded  massive  and  schistose  dolomites  like  those  described 
above.  In  some  places  the  roadbed  passes  through  sohd  ledges  in  open  cuts 
that  exhibit  beautifully  the  massive  character  of  the  rock.     At  the  stream 


ALGONKIAN,  RANDVILLE  DOLOMITE.  265 

crossing  about  400  feet  north  of  the  south  line  of  sec.  35  the  exposures  • 
are  particularly  good,  since  in  addition  to  the  railroad  cut  thei'e  is  here  a 
natural  section  made  by  the  stream  which  tumbles  through  a  little  gorge 
in  a  series  of  small  cataracts  and  rapids.  In  all  its  essential  features  the 
dolomite  here  is  like  that  to  the  south.  It  is  banded  by  thin  parallel  seams 
of  argillaceous  dolomite,  that  extend  from  the  weathered  surfaces  as  little 
projecting  ridges,  and  is  cut  by  the  usual  quartz  veins.  The  strike  is  N. 
85°  W.,  and  the  dip  is  85°  S,  North  of  the  stream  the  road  traverses  a 
swamp  which  drill  holes  show  to  be  underlain  by  Lake  Superior  sandstone 
lying  above  dolomite. 

North  of  the  swamp,  toward  the  center  of  sec.  35,  exposures  again 
begin,  and  extend  north  almost  continuously  on  both  sides  of  the  road  for 
a  distance  of  about  800  feet.  The  ledges  are  usually  small  and  flat  on  the 
east  side  of  the  road  and  somewhat  larger  and  more  knob  like  on  the  west- 
ern side.  There  is  no  regularity  in  the  succes.sion  of  beds  exposed,  though 
slates  and  conglomerates  predominate  toward  the  south  and  dolomites 
toward  the  north.  Traveling  northward,  and  examining  the  ledges  now  on 
one  side  and  now  on  the  other  side  of  the  roadbed,  we  find  first  a  series  of 
black  slates,  dolomitic  quartzites  and  conglomerates,  and  pink  dolomites, 
followed  by  interbedded  gray  slates  and  dolomites,  and  finally  a  succession 
of  thick  beds  of  bluish-gray  dolomite. 

The  black  slates,  quartzites,  conglomerates,  and  dolomites  are 
definitely  interbedded.  The  slates  are  dark-gray,  almost  black,  rocks  with 
thin  laminee  preserving  the  bedding  very  perfectly.  The  cleavage  is 
parallel  to  the  bedding,  which  strikes  about  N.  70°  W.  North  of  the  slate 
ledges  are  others  in  which  the  interbanded  quartzites  and  dolomites  are 
well  exposed.  The  quartzites  are  rather  coarse-grained  pink  varieties 
composed  largely  of  intermingled  quartz  grains  and  crystalline  dolomite. 
Their  beds,  varying  in  thickness  from  a  few  inches  to  2  feet,  weather 
with  a  dark-red  color  and  a  rough  porous  surface.  In  them  are  occasional 
fragments  of  dolomite,  of  a  dark-gray,  fine-grained  rock  resembling  chert 
in  its  general  appearance,  and  of  a  white  or  light-colored  schist  that  looks 
something  like  the  light- colored  slates  associated  with  the  dolomites  farther 
north.  In  a  few  ledges  the  fragments  are  so  abundant  that  the  rock  may 
be  denominated  a  conglomerate.  From  the  relations  of  the  cono-lomerate 
to  the  quartzites  and  the  dolomite,  it  is  clear  that  it  can  mark  no  important 


266  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

stratigraphic  break  in  the  series.  It  is  intrafoi'mational.  The  dolomite 
interstratified  with  the  quartzites  and  conglomerates  is  also  pink  in  color. 
On  fresh  fractures  the  principal  difference  noted  between  the  first  two 
rocks  named  is  the  finer  grain  of  the  dolomite  and  less  abundance  of  quartz 
grains  in  it.  Quartz  is  present,  however,  but  only  in  small  grains  and  in 
no  great  quantity.  The  weathered  surface  of  the  dolomite  is  depressed 
below  that  of  the  quartzite  and  its  texture  is  much  more  finely  granular. 
Ledges  in  which  both  rocks  occur  have  therefore  a  corrugated  surface 
made  up  of  projecting  bands  of  a  coarsely  granular  structure  alternating 
with  depressed  bands  of  a  finely  granular  structure. 

Farther  north  slates  again  appeal'.  These,  however,  are  unlike  the 
dark  slates  to  the  south.  They  are  usually  light  gray,  more  or  less 
schistose  rocks  containing  considerable  dolomite,  constituting  beds  from  a 
few  inches  to  50  feet  in  thickness.  In  all  their  essential  features  they 
resemble  very  closely  the  slates  associated  with  the  Kona  dolomite  in  the 
Marquette  district."  None  of  the  wider  beds  are  composed  exclusively  of 
slate.  There  are  always  interlaminated  with  this  rock  thin  seams  of  dolo- 
mite, but  the  slate  predominates.  Alternating  with  the  beds  composed 
principally  of  slates  are  others  composed  exclusively  of  dolomite.  As  we 
proceed  northward  we  find  the  dolomite  becoming  more  prominent,  the 
northernmost  ledges  consisting  exclusively  of  this  rock.  The  dolomites  in 
this  portion  of  the  section  are  schistose  bluish-gray  varieties  interlaminated 
with  thin  layei's  of  a  more  siliceous  phase  that  projects  above  the  general 
surfaces  of  the  ledges  as  dark-red  ridges  no  thicker  than  sheets  of  wrapping 
paper.  In  many  places  the  ridges  are  crinkled  and  closely  folded,  while 
the  dolomite  between  them  seems  to  be  quite  devoid  of  any  evidences  of 
minor  contortions.  The  schistosity  of  the  dolomite  strikes  N.  70°  to  80° 
W.  and  dips  70°  to  80°  S.;  i.  e.,  it  is  concordant  with  that  of  the  rock 
elsewhere  throughout  this  portion  of  the  district.  In  some  ledges  the 
bedding  and  schistosity  strike  and  dip  in  the  same  directions,  but  in  most 
exposures  the  two  structures  intersect  each  other  at  greatly  varying 
angles,  the  strike  of  the  bedding  cliangiug  rapidly  within  short  distances. 
In  the  two  small  ledges  on  opposite  sides  of  the  roadbed  at  the  northern 
end  of  the  section  definite  folds  pitching  to  the  west  are  plainly  apparent. 
In  the  ledge  on  the  west  side  of  the  road  the  schistosity  strikes  N.  85° 

a  Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897,  pp.  244-245,  259-260. 


ALGONKIAN,  RANDVILLE  DOLOMITE.  267 

W.  and  dips  78°  to  80°  N.  This  is  the  most  prominent  structure  and 
the  one  most  easily  discerned  in  the  ledge.  Close  inspection  will  show, 
however,  that  the  little  projecting  quartzose  layers  referred  to  above  do  not 
always  run  in  this  direction,  but  that,  on  the  contrary,  they  frequently 
depart  from  it  very  widely,  the  variation  in  the  two  directions  sometimes 
amounting  to  90°.  Since  these  bands  mark  the  bedding,  it  becomes  plain 
that  while  the  two  structures,  bedding  and  schistosity,  coincide  in  some 
places,  in  others  they  are  distinct,  and  the  difference  is  due  to  the  variation 
in  the  bedding.  An  inspection  of  the  bedding  shows  a  fold  pitching  to  the 
west  at  an  angle  of  35°  to  40°,  which  accounts  completely  for  the  discrep- 
ancies noted  in  the  two  structures.  On  the  east  side  of  the  road  a  similar 
condition  obtains,  except  that  the  strike  of  the  schistosity  is  N.  70°  W.  and 
its  dip  70°  S.,  and  the  pitch  of  the  fold  30°  to  40°  W.  The  presence  of 
minor  folding  at  this  place  has  been  used  as  an  argiiment  in  favor  of  the 
existence  of  a  larger  fold  in  the  series  (see  p.  247). 

Northwest  quarter  of  sec.  9,  T.  39  N.,  B.  29  TF.— The  south  half  of  this 
quarter  section  is  underlain  by  the  iron-bearing  Upper  Menominee  beds 
and  by  Hanbury  slates.  In  its  north  half  are  magnificent  exposures  of  the 
dolomite  formation,  showing  nearly  all  of  its  phases,  except  some  of  the 
slaty  ones.  Just  east  of  the  Aragon  shaft  No.  1  is  the  mouth  of  a  little 
gully  about  130  paces  wide  (see  PI.  XXXIII),  which  extends  a  few  degrees 
south  of  east  for  about  a  quarter  of  a  mile.  Its  north  side  and  east  end  are 
bounoled  by  high  and  almost  precipitous  ledges  of  dolomite  and  its  south 
side  by  a  low  ridge  of  jaspilite  and  quartzite  belonging  with  the  Vulcan 
iron  formation.  The  latter  will  be  described  in  another  place  (j).  435). 
The  floor  of  the  gully  is  flat  and  even.  It  is  now  occujjied  as  a  little 
garden  patch,  but  was  evidently  once  more  or  less  swampy  It  is  probably 
underlain  in  part  at  least  by  talcose  schists.  The  cliffs  on  the  north  side  of 
the  valley  rise  abruptly  from  the  valley  floor  to  a  height  of  about  50  feet, 
forming  the  south  side  of  a  little  range  of  rough  hills  which  separate  this 
valley  from  the  great  plain  that  extends  eastward  from  the  open  pits  of  the 
Norway  and  Perkins  mines.  The  hills  are  nearly  bare  of  vegetation, 
but  a  light  covering  of  soil  obscures  the  relations  of  the  rocks  to  a  consid- 
erable extent.  Bedded  and  brecciated  dolomites,  brecciated  cherts,  and  a 
few  light-colored  slates  constitute  the  principal  rock  types  exposed.  For 
the  most  part  the  distinctly  bedded  rocks  strike  about  N.  65°  "W.  and  dip 


268  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

between  40°  and  50°  S.,  but  at  the  eastern  and  western  ends  of"  the 
range  the  rocks  are  in  phmging  folds  that  naturally  cause  rapid  variations 
in  strikes  and  dips.  In  many  ledges,  moreover,  even  where  the  dolomite 
layers  have  a  uniform  strike,  the  slates  interbedded  with  these  are  deformed 
into  many  little  folds. 

In  the  little  hillock  at  the  west  end  of  the  ridge  the  folding  is  very 
pronounced.  On  the  top  of  the  hillock  dolomites  and  slates  are  well 
exposed,  with  strikes  varying  between  N.  S'^°  E.  and  N.  70°  W.  and  dips 
between  30°  and  45°  S.  Small  folds  are  abundant  in  the  slates,  and 
several  larger  ones  affect  the  slates  and  dolomites  alike.  On  the  east  side 
of  the  exposed  surface  these  pitch  to  the  west  and  on  the  west  side  they 
pitch  to  the  east. 

Southeast  of  this  exposure  is  another  one  forming  a  westward-facing 
bluff.  In  this  the  strike  of  the  dolomite  beds  varies  from  north  on  the 
northwest  side  of  the  cliff  through  N.  45°  W.  to  N.  70°  W.  on  its  south 
side.  The  dip  varies  between  25°  and  80°  SW.  At  this  place  there  is 
evidently  a  fold  pitching  faii'ly  steeply  to  the  west.  At  its  apex,  i.  e., 
between  the  points  at  which  the  strikes  are  north  and  northwest,  the  rock 
is  shattered  and  a  well-marked  dolomite-breccia  has  developed. 

From  the  south  side  of  this  bluff  dolomites  extend  eastward  with  a 
uniform  strike  of  about  N.  70°  W.  and  a  dip  of  about  40°  to  50°  for  about 
500  paces,  forming  the  line  of  little  cliffs  bordering  the  north  side  of  the 
valley.  Similar  rocks  with  the  same  strikes  and  dip  likewise  constitute  the 
north  slojDO  of  the  ridge.  The  top  of  the  ridge  consists  of  chert.  This 
begins  at  a  point  between  the  two  little  hillocks  above  referred  to  as 
exhibiting  folds,  and  stretches  as  an  almost  continuous  ledge  the  entire 
length  of  the  ridge  and  finally  disappears  under  the  soil.  On  both  sides  it 
is  flanked  by  the  dolomite  forming  the  north  and  the  south  slopes  of  the 
ridge.  The  chert  ajjpears  on  fresh  surfaces  as  a  fine-grained  rock  mottled 
with  gray,  red,  blue,  and  white  streaks,  and  cut  by  short  cracks  the  walls  of 
which  are  coated  by  druses  of  tiny  quartz  crystals.  On  surfaces  that  have 
been  exposed  to  the  weather  a  brecciated  structure  becomes  very  apparent 
and  the  irregular  mottling  observed  on  the  fresh  surfaces  is  seen  to  be  due 
to  the  presence  of  white  and  bluish-gray  fragments  cemented  together  by 
a  reddish  groundmass.  Nearly  all  the  chert  in  these  hills  seems  to  be 
brecciated  in  this   way.     The  brecciation  does    not  appear   to  bear  any 


ALGONKIAN,  RANDVILLE  DOLOMITE.  26Q 

definite  relation  to  the  axes  of  folds.  Although  best  exhibited  where  folds 
are  recognizable  in  the  associated  dolomites,  it  is  by  no  means  hmited  to 
these  positions.  Here  as  elsewhere  the  chert  seems  to  be  characterized  by 
the  brecciated  structure,  as  though  its  brittleness  caused  it  to  yield  to 
compressing  stresses  more  easily  by  fracture  than  by  flowage  even  when 
confined  between  dolomite  beds  that  were  deformed  by  flowage  exclusively. 

At  the  east  end  of  the  ridge  the  relations  of  cherts  and  dolomites 
again  become  complicated.  From  the  northeast  corner  of  the  main  valley, 
where  the  cliff's  bordering  its  north  side  meet  those  bordering  its  east  end, 
two  little  side  valleys  or  ravines  extend  northward.  The  more  westerly  one 
afi'ords  an  excellent  section  through  the  ridge  at  a  point  where  the  folding 
seems  to  be  the  most  complicated— indeed  it  appears  that  the  ravine  is  a 
consequence  of  the  folding.  The  west  side  of  the  ravine  is  a  bluff"  exposing 
a  sharp  fold  in  dolomites  overturned  to  the  north  and  pitching  to  the  east. 
On  its  south  face,  overlooking  the  main  valley,  the  dolomite  has  the  normal 
strike,  N.  70°  W.,  and  a  dip  of  40°  S  Passing  northward  along  the  edge 
of  the  bluff",  however,  the  strike  is  observed  to  swing  to  the  east,  and  then  to 
become  northeast,  north,  and  northwest,  successively,  and  finally  to  resume 
a  direction  on  the  north  side  of  the  hill  parallel  to  that  observed  on  its 
south  side,  i.  e.,  N.  70°  W.  Where  the  strike  is  approximately  noi^li,  i.  e., 
at  the  point  which  may  be  supposed  to  be  in  the  axis  of  the  fold,  the  dip  is 
30°  N.  On  the  north  limb  of  the  fold  the  dip  corresponds  to  that  on 
the  south  limb,  viz,  40°  S. 

Beyond  this  fold,  on  the  top  of  the  ridge,  even-bedded  dolomites  with 
the  usual  strike  and  dip  are  again  exposed  in  a  large  ledge,  and  in  contact 
with  them  to  the  east  appear  equally  large  exposures  of  the  chert.  The 
dolomite  is  apparently  the  continuation  of  the  beds  flanking  the  north  side 
of  the  chert  band  on  top  of  the  ridge  to  the  west.  The  chert,  on  the  other 
hand,  seems  to  be  a  distinct  bed,  quite  independent  of  the  beds  on  the  top 
of  the  ridge,  though  it  may  possibly  be  the  same  bed  repeated  by  folding 
or  faulting.  This  chert  extends  practically  continuously  for  about  150 
paces  to  the  southeast,  and  is  in  contact  on  its  south  side  with  bedded 
dolomite  and  dolomitic  and  cherty  breccias.  On  its  west  side  its  contact  is 
with  the  dolomite  forming  the  north  slope  of  the  ridge,  as  already  men- 
tioned. This  contact  is  extremely  sharp.  It  cuts  diagonally  across  the 
bedding  of  the  dolomite,  so  that  the  chert  rests  directly  upon  the  truncated 


270  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

layers  of  this  rock.  From  the  relations  of  the  chert  to  the  dolomite  else- 
where it  is  plain  that  the  two  rocks  are  not  separated  by  an  unconformity, 
nor  is  it  probable  that  the  chert  in  this  instance  occurs  as  a  vein  in  the 
dolomite.  The  phenomenon  is  best  explained  as  due  to  the  presence  of  a 
little  fault  along  the  contact  line.  On  the  east  wall  of  the  httle  ravine, 
opposite  the  exposures  just  described,  are  others  of  the  same  character. 
Dolomitic  breccias  are  particularly  well  developed  here,  the  picture  repro- 
duced in  PI.  XVI,  A,  exhibiting  the  appearance  of  one  of  them,  in  which 
the  fragments  and  matrix  are  practically  all  dolomite.  On  the  top  of  the 
bluff  the  breccia  can  be  seen  to  be  interbedded  with  nonbrecciated  dolo- 
mites. Evidence  of  folding  is  as  marked  on  this  wall  of  the  ravine  as  on 
the  western  wall,  but  the  exposures  are  not  as  continuous,  and  consequently 
the  character  of  the  folding  can  not  be  as  well  worked  out.  It  is  probable 
that  the  folds  pitch  to  the  Avest.  Since  the  dip  in  the  dolomite  beds 
immediately  to  the  north  of  the  breccia  figured  (PI.  XVI,  A)  is  to  the  north 
and  that  in  the  bed  to  the  south  is  southerly,  it  is  possible  that  the  brec- 
ciated  band  is  situated  along  the  axis  of  the  fold.  However,  in  other 
portions  of  the  hills  smaller  exposures  of  the  same  khid  of  breccias  are 
frequently  met  with  in  which  the  relations  to  folding  are  not  so  plain.  It 
is  true  that  in  almost  all  these  cases  departures  from  the  normal  dips  and 
strikes  may  be  observed,  but  it  is  not  always  certain,  or  even  probable,  that 
the  breccias  mark  the  axis  of  the  folds. 

From  the  distribution  of  the  folds  and  of  the  breccias,  and  from  the 
relations  of  the  latter  to  the  former,  as  well  as  the  relations  of  the  cherts 
to  the  dolomites  it  would  seem  that  the  dolomite  series  in  this  range  of  hills 
is  affected  by  a  close  east-west  folding  and  a  more  open  north-south  fold- 
ing, with  occasionally  subordinate  faulting.  The  chert  is  apparently  inter- 
bedded with  the  dolomite  near  but  not  at  the  top  of  the  series.  That  this 
folding  is  connected  with  that  which  gave  rise  to  the  Norway  and  Aragon 
ore  basins  can  admit  of  no  doubt. 

The  cliffs  at  the  east  end  of  the  main  ravine  consist  exclusively  of 
well-bedded  dolomites  striking  uniformly  about  N.  65°  W.  and  dipping 
35°  to  40°  S.  At  the  extreme  southeast  corner  of  the  ravine  the  strike 
becomes  more  nearly  east-west  (N.  85°  W.)  and  the  dip  higher  (50°).  To 
the  east  and  to  the  west  of  this  exposure  are  several  pits  in  iron-formation 
material  which  are  ]ust  a  trifle  south  of  the  projection  of  the  strike  of  the 


ALGONKIAN,  KANDVILLE  DOLOMITE.  271 

southehimost  portion  of  the  ledge.  This  fact  indicates  that  the  ledge  is  very 
near  the  contact  of  the  dolomite  formation  with  the  iron-bearing  Vulcan 
formation.  No  direct  contact  is  observable,  but  by  digging  into  the  little 
gully  that  runs  down  the  cliff  on  the  south  side  of  the  dolomite  exposure 
large  loose  pieces  of  a  white  quartzite  conglomerate  containing  numerous 
jasper  fragments  may  be  picked  from  the  soil.  The  abundance  of  these 
fragments  and  the  fact  that  they  comprise  the  only  kinds  found  in  this  place 
jioint  to  the  conclusion  that  the  ledge  from  which  they  were  separated 
is  but  a  short  distance  beneath  and  that  the  rock  marks  an  unconformity 
between  the  dolomite  and  the  overlying  iron  formation. 

Sees.  12  and  13,  T.  39  N.,  B.  29  W. — The  most  extensive  exposures  of 
the  dolomite  series  is  in  the  group  of  hills  and  hillocks  in  the  valley  of  the 
Sturgeon  River,  sees.  12  and  13,  T.  39  N.,  R.  29  W.  The  ledges  are  almost 
bare  of  vegetation,  and  therefore  present  exceptionally  favorable  opportuni- 
ties for  study.  Those  in  sec.  13  are  near  the  north  quarter  post  of  the 
section,  just  north  of  the  wagon  road  from  Vulcan  to  Loretto,  on  the  south 
side  of  a  high  hill,  the  top  of  which  in  all  probability  is  covered  with  the 
Lake  Superior  sandstone  (see  PI.  XLI).  A  walk  of  a  quarter  of  a  mile  due 
north  will  bring  one  to  the  principal  group  of  ledges,  lying  between  the 
front  of  the  hill  just  referred  to  and  the  track  of  the  Escanaba  and  Iron 
Mountain  Railroad  (Chicago  and  Northwestern),  one-fourth  mile  farther 
north.  Most  of  the  ledges  are  small,  flat  exposures,  but  here  and  there  a 
little  hillock  rises  from  the  valley  floor,  and  on  the  south  side  of  the  railroad 
a  very  large,  bare,  smooth  knob  lifts  its  top  about  75  feet  almost  vertically 
above  the  rails.  It  is  an  almost  solid  ledge  of  dolomite,  but  at  its  eastern 
end,  where  its  slope  is  gradual,  the  rock  is  covered  with  drift  material.  This 
larsre  ledsre  and  the  smaller  ones  to  the  south  afford  an  almost  continuous 
exposure  of  the  series  for  a  distance  of  about  600  paces  across  its  strike. 
The  distance  from  the  southernmost  ledge,  near  the  wagon  road,  to  the 
northernmost  one,  in  the  center  of  sec.  12,  on  the  side  of  the  railroad  track, 
is  about  3,100  feet. 

From  the  center  of  the  section  the  ledges  extend  eastward  toward  the 
lower  portions  of  the  Sturgeon  Valley,  where  they  are  buried  beneath 
thick  deposits  of  sands.  On  the  east  side  of  the  river,  however,  the  rocks  of 
the  series  again  emerge  from  beneath  the  sands  and  outcrop  in  a  number 
of  small  hills  in  the  northeast  quarter  of  sec.  13,  T.  39  N.,  R.  29  W.,  and  in 


272  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  southwest  quarter  of  sec.  7  and  the  north  half  of  sec.  18,  in  T.  39  N., 
R.  28  W.  A  network  of  roads  radiating  from  the  bridge  across  the 
Sturgeon  on  the  main  road  from  Loretto  to  Waucedah  passes  between 
the  outcrops  and  approaches  many  of  tliem  so  closely  that  they  may  be 
examined  from  the  seat  of  a  carriage.  These  outcrops  are  not  as  interesting 
as  those  on  the  west  side  of  the  river,  however,  as  they  consist  almost 
uniformly  of  a  heavy-bedded,  almost  massive  dolomite,  striking  and  dipping 
in  uniform  directions.  / 

The  southernmost  dolomite  ledge  in  sec.  13  is  situated  about  200  paces 
south  of  the  north  quarter  post  of  the  section  and  about  75  paces  north 
of  a  deep  shaft  in  the  iron  formation,  from  which  a  large  quantity  of  poor 
ore  has  been  taken.  The  ledge  is  made  up  of  alternating  bands  of  pink 
and  dark  reddisli-bi-own  dolomite  striking  N.  85°  E.  and  dipping  70°  S. 
The  lighter-colored  bands  are  divided  into  layers  by  very  thin  seams  of 
darker  color,  and  are  traversed  by  little  joint  cracks  and  fault  planes.  In 
many  places  the  fine  bedding  lines  show  distinct  contortions,  which, 
however,  are  not  observable  in  the  broader  bands.  In  other  words,  while 
the  broad  bands  of  dolomite  have  a  uniform  strike  and  dip  throughout  the 
ledge,  they  exhibit  within  themselves  complex  minor  corrugations.  In  some 
instances  the  corrugations  are  so  sharp  that  the  contorted  bands  are 
actually  fractured  and  the  rock  becomes  a  breccia. 

Another  ledge  just  east  of  the  quarter  post  is  a  more  typical  dolomite 
breccia  than  that  just  described.  On  the  weathered  surface  angular 
fragments  of  pink  dolomite  and  others  with  rounded  edges  are  seen  to  be 
separated  from  one  another  by  stringers  and  small  triangular  patches  of  a 
dark-colored  sandy  nature.  Where  the  rock  is  not  brecciated  it  is 
contorted  in  the  most  complex  way.  E-sadently  a  breccia  of  this  kind  was 
formed  by  mechanical  means  after  the  rock  itself  had  been  laid  down  as  a 
series  of  alternating  layers  of  dolomite  and  dolomitic  quartzite. 

The  ledges  in  the  northern  portion  of  the  south  half  of  sec.  12  are 
composed  of  interbedded  dolomites,  dolomitic  quartzites,  and  slates.  In 
the  southernmost  ledge,  on  the  north-south  quarter  line  of  the  section,  for 
instance,  are  to  be  found  a  15-foot  bed  of  dark,  pinkish-gray,  thin-bedded 
dolomitic  quartzite,  interlaminated  with  thin  bands  of  a  bluish-gray  slate,  a 
bed  of  purple  dolomite  12  feet  thick,  interbanded  with  thin  seams  of  a  light- 
gray  slate,  a  7-foot  bed  of  coarse  dolomitic  quartzite  containing  thin  beds 
of  dolomite,  a  band  of  dolomite  and  slate  25  feet  wide,  10  feet  of  quartzite, 


ALGONKIAN,  NEGAUNEE  FORMATION.  273 

and  10  feet  of  dolomite.  The  bedding  of  all  these  rocks  strikes  N.  65°  to 
70°  W.  and  dips  45°  to  52°  S. 

As  we  pass  northward  the  sandstones  and  slates  become  less  prominent 
and  the  dolomites  more  abundant.  The  hill  next  north  of  the  ledare 
described  in  the  last  paragraph  is  composed  of  interlaminated  dolomite  and 
thin  beds  of  slate.  The  rocks  strike  as  in  the  ledge  to  the  south,  but  the 
dips  vary  from  50°  S.  to  nearly  horizontal.  The  steeper  dips  occur  on  the 
slopes  of  the  hill  and  the  flat  ones  on  top.  In  places,  however,  on  the  top 
the  layers  are  closely  folded  into  sharp  little  folds,  pitching  very  steeply, 
the  westernmost  ones  to  the  west  and  the  easternmost  ones  to  the  east. 

North  of  this  hillock  only  thick-bedded  dolomites  appear.  These 
rocks  form  the  large  hill  already  referred  to  as  being  south  of  the  railroad 
track  in  the  center  of  the  section.  Bedding  lines  with  a  dip  of  45°  S.  can 
be  observed  on  the  southern  side  of  the  hill.  As  we  pass  north  over  the  hill 
the  dolomite  becomes  more  and  more  massive  until  on  the  ridge  no  distinct 
strikes  nor  dips  are  noticeable.  On  the  cliff  overhanging  the  track,  how- 
ever, the  dip  is  vertical  in  one  place  and  at  its  east  end  there  is  an  exposure 
with  a  dip  to  the  south.  North  of  this  ledge  there  are  no  exposures  for 
some  distance.  The  outlook  from  the  top  of  the  hill  is  over  a  swamp,  bor- 
dered on  the  north  by  a  steep  sand  slope  leading  upward  to  a  sand  plateau. 

This  section  aiforded  the  data  for  the  best  estimate  of  the  thickness  of 
the  Randville  formation  that  was  obtained. 

NEGAUNEE  FORMATION. 

The  identification  of  an  iron-bearing  formation  in  the  Lower  Menom.- 
inee  series  corresponding  to  the  Negaunee  formation  of  the  Lower  Mar- 
quette series  in  the  Marquette  and  Felch  Mountain  districts  is  based  mainly 
on  the  fact  that  the  lower  layers  of  the  Upper  Menominee  series  contain 
fragments  of  jasper  and  ore  that  must  have  been  derived  from  an  older 
series.  Whether  the  formation  that  yielded  these  fragments  was  exactly 
equivalent  to  the  Negaunee  formation  in  the  Marquette  district  or  not  can 
not  be  definitely  determined;  but  it  must  have  rested  upon  the  Randville 
dolomite  and  occurred  below  the  Upper  Menominee  Vulcan  formation, 
which  in  many  places  is  immediately  above  the  dolomite,  for  jaspilites  are 
not  known  in  the  Archean  rocks  surrounding  the  Menominee  trough  nor  in 
the  Huronian  beds  below  the  top  of  the  Randville  formation.  The  position 
MON  XLVI — O-t 18 


274  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

of  this  supposed  formation  in  the  Menominee  district  corresponds  exactly 
with  that  of  the  Negaunee  formation  in  the  Marquette  district.  No  dis- 
tinctive name  has  been  given  it  in  the  Menominee  district,  because  of  the 
impossibihty  of  deciding  positively  whether  or  not  there  ai'e  any  remnants 
of  it  now  exposed  on  the  surface.  It  must,  however,  be  refeiTcd  to  in  any 
discussion  on  the  geology  of  the  district,  because  only  on  the  assumption 
of  its  presence  can  be  exjjlained  some  of  the  deposits  of  ore  and  jasper  in 
the  Upper  Menominee  series. 

The  jaspilites  described  in  the  immediately  succeeding  pages,  while 
probably  members  of  the  Vulcan  formation  of  the  Upper  Menominee  series, 
are  nevertheless  somewhat  di  .Terent  in  their  lithological  features  from  the 
other  jaspilites  of  the  formation,  and  very  like  those  in  the  Negaunee 
formation  in  the  Marquette  district.  They  are  also  very  similar  to  the 
jasper  in  the  pebbles  of  the  coarse  quartzite  at  the  base  of  the  Vulcan  beds, 
and  therefore  must  be  similar  to  the  jaspilites  tliat  furnished  these  pebbles. 
For  these  reasons  they  are  discussed  at  greater  length  than  their  areal 
importance  in  the  district  would  otherwise  warrant,  and  not  because  it  is 
believed  that  they  are  actually  remnants  of  Negaunee  beds  that  have 
escaped  erosion.  The  Negaunee  jaspilites  were  like  these  in  all  essential 
respects,  and  so  the  latter  may  serve  to  illustrate  the  features  of  the  former. 

DISTRIBUTION. 

Remnants  of  the  Negaunee  formation  may  exist  in  the  Aragon  mine, 
the  Pewabic  mine,  and  some  of  the  other  mines  of  the  district,  but  of 
this  we  have  no  definite  knowledge,  as  the  mining  plats  can  not  discrim- 
inate between  two  iron  formations  so  nearly  alike  in  their  macroscopical 
features  as  are  those  of  the  supposed  Negaunee  and  the  Vulcan  foi-matious. 
The  exposures  above  referred  to,  consisting  of  a  jaspilite  similar  to  that 
which  furnished  the  pebbles  to  the  basal  conglomerate  in  the  Upper 
Menominee  series,  lie  in  a  narrow  belt  bordering  the  south  side  of  the 
Randville  dolomite  area  near  the  center  of  sec.  9,  T.  39  N.,  R.  29  W.  (see 
map,  PL  XXXIII).  This  belt  is  outlined  b}^  three  test  pits,  a  ledge,  and 
several  large  abandoned  mining  pits.  It  begins  a  short  distance  east  of  the 
shaft  of  the  old  Brier  Hill  mine,  embraces  the  north  portion  of  the  large, 
flat  exposure  lying  a  few  degrees  north  of  east  of  Curry  shaft  No.  2,  and 
ends,  so  far  as  observed,  at  the  northwest  corner  of  the  old  mining  pit  No.  3 
in  the  center  of  the  southeast  quarter  of  the  northwest  quarter  of  sec.  9. 


ALGONKIAN,  NEGAUNEE  FORMATION.  275 

LITHOLOOY. 

The  rocks  from  the  naiTOw  belt  of  iron  formation  just  mentioned 
comprise  even-banded  beds  of  jasper  and  ore  which  have  a  range  in  thick- 
ness from  the  fraction  of  an  inch  to  three  inches  or  more.  The  jasper, 
which  is  of  a  dark  purphsh-i-ed  color,  is  very  fine  grained.  It  has  a  flinty 
texture  and  a  completely  homogeneous  aspect.  Here  and  there  it  is  cut  by 
little  cracks  lined  with  small  plates  of  brilliant  hematite.  Sometimes  the 
rock  is  fai;lted  and  hematite  has  penetrated  between  the  faulted  surfaces. 
The  ore  interlaminated  with  the  jasper  is  a  hard,  dense,  finely  granular 
hematite,  often  possessing  a  slaty  cleavage,  but  rarely  exhibiting  a  specular 
character.  It  is  sometimes  spangled  with  tiny,  brilliantly  reflecting  crystals 
of  hematite,  that  appear  to  be  due  to  infiltration,  and  sometimes  it  contains 
a  small  quantity  of  minute  magnetite  crystals.  While  some  of  the  ore 
bands  are  homogeneous  tln-oughout,  most  of  them  when  examined  carefully 
are  observed  to  be  made  up  of  interlaminations  of  very  thin  layers  of  ore 
and  jasper.  The  contact  between  the  hematite  and  the  jasper  layers  is 
usually  sharp  and  even,  and  often  the  rock  will  split  more  easily  along  this 
contact  plane  than  anywhere  else.  Frequently,  however,  there  is  a  gradation 
between  the  lasers,  the  jasper  near  the  ore  bands  becoming  more  and  more 
thickly  impregnated  with  hematite  until  it  is  apparently  replaced  entirely 
by  the  iron  oxide.  The  ore  layers,  like  the  jasper  beds,  are  traversed  by 
cracks  lined  by  hematite  crystals,  producing  bright,  glistening  streaks  across 
the  dull  surface  of  the  ore.    Both  ore  and  jasper  are  cut  by  tiny  veins  of  quartz. 

In  natural  light  sections  of  the  jasper  appear  to  be  composed  of  a 
uniform  aggregate  of  colorless  quartz  grains  elongated  in  a  common 
direction,  which  is  parallel  to  the  bedding,  crystals  and  aggregates  of 
crystals  of  blood-red  hematite,  a  few  small  flakes  of  some  micaceous  min- 
eral, and  an  abundance  of  hematite  dust  particles.  Their  most  noticeable 
structural  feature  is  the  presence  of  numerous  little  oval  masses  or  lenseS 
arranged  in  lines  that  are  parallel  to  the  bedding.  The  lenses  are  all 
elongated  in  this  same  direction,  and  are  separated  from  one  another  by  a 
groundmass  without  distinctive  structure  other  than  the  schistosity  due  to 
the  elongation  of  the  quartz  grains.  The  lenticular  areas  are  composed  of 
the  same  kind  of  quartz-hematite  aggregate  as  that  composing  the  ground- 
mass  in  which  they  lie.  The  distinguishing  characteristics  that  mark  them 
off  from  the  surrounding  material  are  a  greater  richness  in  hematite 
crystals  and  sometimes  a  difterence  in  the   coarseness  of  grain  of  their 


276  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

quartzose  component  as  compai'ed  with  that  of  the  groundmass  quartz. 
Moreover,  in  some  instances  the  ore  in  the  lenses  is  in  a  different  form  from 
that  of  the  ore  in  the  groundmass.  The  former  is  frequently  in  rods  that 
may  be  the  cross  sections  of  flat  rhombohedra,  while  the  latter  is  in  plumper 
crystals,  whose  cross  sections  are  more  nearly  square.  In  many  instances, 
also,  the  presence  of  the  lenses  is  emphasized  by  the  fact  that  there  is  an 
accumulation  of  ore  particles  near  their  peripheries  which  seems  to  mark 
their  outlines  very  distinctly. 

Between  crossed  nicols  the  sections  break  up  into  an  almost  uniform 
mosaic  of  interlocking  quartz  grains,  many  of  which  exhibit  strain  shadows. 
The  hematite  grains  occur  indiscriminately  between  the  quartzes,  and 
inclosed  within  them.  No  distinction  can  be  noted  between  the  quartz  of 
the  lenses  and  that  of  the  groundmass,  except  that  occasionally  the  latter 
is  a  little  coarser  than  the  former.  There  is  no  sharp  line  of  demarca- 
tion between  the  two.  The  mosaic,  in  most  instances,  seems  to  continue 
uninterruptedly  from  lens  to  groundmass,  and  many  grains  seem  to  lie 
partly  within  the  lens  and  partly  without.  The  mosaic  is  plainly  a  crystal- 
line aggregate;  no  trace  of  a  fragmental  grain  can  anywhere  be  detected  in  it. 

It  is  extremely  difficult  to  reconstruct  the  original  clkaracter  of  the 
rock.  The  lenses  may  be  regarded  either  as  mashed  jasper  fragments  that 
lay  in  a  finer-grained  quartzite,  or  as  having  been  originally  concretionary 
masses  in  a  cherty  sediment,  such  as  gave  rise  to  the  jaspilites  of  the 
Penokee  district  and  those  belonging  in  the  Negaunee  formation  of  the 
Marquette  district.  Whatever  the  original  character  of  the  rock,  it  has  been 
so  completely  silicified  that  definite  traces  of  its  structure  have  disappeared. 
From  the  fact,  however,  that  in  a  silicified  quartzite  the  fragmental  cores 
of  quartz  to  which  the  new  quartz  was  added  can  in  almost  all  cases  be 
detected,  whereas  none  have  been  recognized  in  the  jaspers  under  discus- 
sion, it  is  concluded  that  the  rock  can  not  have  been  a  quartzite  made  up 
partly  of  jasper  fragments.  From  analogy  with  the  Penokee  and  Marquette 
jaspilites,  and  because  the  rocks  ai'e  like  many  of  the  concretionary  jaspilites 
from  these  districts,  except  that  they  are  more  squeezed,  it  is  thought  that 
the  lenses  noted  in  the  Menominee  jaspers  may  be  mashed  concretions 
and  the  jaspers  themselves  may  be  silicified  rocks  comprised  largely  of 
ferruginous  carbonates  or  of  greenalite. " 

"  These  lenses  are  identical  in  every  respect  with  those  pictured  by  Leith  in  The  Mesabi  iron- 
bearing  district  of  Minnesota:  Mon.  U.  S.  Geol.  Survey,  vol.  43,  1903,  PI.  XV,  C'and  D,  and  regarded 
by  him  as  being  altered  greenalite  grains. 


ALGONKIAN,  NEGAUNEE  FORMATION.  277 

While  the  defavmation  of  the  jaspers  is  due  principally  to  mashing,  never- 
theless there  has  been  some  crushing.  A  few  quartz  veins  cut  thi'ough  them  in 
several  directions,  most  commonly  in  a  direction  nearly  perpendicular  to  the 
schistosity.  A  few  tiny  veins  filled  with  hematite  are  detected  and  some  of 
the  little  lenses  are  broken  into  pieces  and  faulted.  These  phenomena  were 
evidently  produced  subsequent  to  the  mashing  and  the  resulting  schistosity. 

The  ore  bands  associated  with  the  jasper  dUfer  from  the  latter  mainl}' 
in  the  presence  of  a  much  g-reater  quantity  of  hematite.  This,  is  usually  in 
long,  irregularly  shaped  stringers  running  parallel  to  the  bedding.  The 
stringers  consist  of  open  aggregates  of  crystals  united  at  a  few  points  only 
and  of  masses  made  up  of  crystals  fused  together  compactly.  Occasionally 
these  rod-like  aggregates  are  in  curved  lines,  as  though  they  originally 
suiTounded  a  waterworn  grain  or  a  concretion.  The  relation  of  the 
hematite  to  the  quartz  is  difficult  to  determine,  but  from  the  fact  that  the 
former  is  idiomorphic  with  respect  to  the  latter  wherever  the  two  are  in 
contact,  and  the  further  fact  that  toward  the  ends  of  the  ore  aggregates 
individual  crystals  of  the  hematite  are  to  be  seen  embedded  in  quartz 
grains,  it  is  concluded  that  most,  if  not  all,  the  hematite  is  older  than  the 
quartz.  The  relations  between  the  ore  and  the  quartz  are  exactly  the  same 
as  those  existing  in  the  ferruginous  cherts  of  the  Negaunee  formation  in  the 
Marquette  district  where  "there  is  no  apparent  concentration  of  the  iron 
oxides  between  the  quartz  grains,  but  they  occur  concentrated  in  laminae 
or  as  separate  flecks  included  in  the  grains  of  quartz  just  as  though  they 
were  all  in  their  present  positions  before  the  silica  began  to  crystallize." " 

RELATIONS  TO  ADJACENT  FORMATIONS. 

The  contacts  of  the  jaspilites  with  the  underlying-  rocks  are  covered. 
The  relations  of  the  Negaunee-like  jaspilites  with  others  that  are  unques- 
tionably members  of  the  Uj^per  Menominee  series  are  well  seen  in  the  ledge 
east  of  Curry  shaft  No.  2.  On  the  north  side  of  the  ledge  the  jaspilites 
are  of  the  character  described  above.  On  the  south  side  they  are  more 
nearly  like  the  jaspilites  characterizing  some  portions  of  the  Traders 
member  of  the  Vulcan  formation.  The  jasper  layers  particularly  are 
more  granular  and  less  vitreous  than  those  to  the  north,  and  tliey  are 
frequently    mottled    with    little    oval    spots    of   a    bright-red    color.     The 

«Mon.  r.  S.  Geo].  Survey,  vol.  28,  1897,  p.  370. 


278  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

northern  jasper  is  dull  red  and  breaks  with  a  conchoidal  fracture.  The 
southern  jasper,  while  red  on  the  weathered  surface,  is  darker  on  the  fresh 
fracture,  and  has  a  grayish-purple  color.  Moreover,  it  breaks  with  an 
uneven,  fragmental  aspect,  the  surface  being  roughened  by  little  projecting 
splinters  with  a  white  color  and  a  granular  texture.  All  the  rocks  strike 
uniformly  N.  85°  W.  and  dip  82°  S.  at  the  west  end  of  the  exposure,  and 
strike  N.  70°  W.  and  di))  60°  S.  at  its  east  end.  At  the  two  extremities  of 
the  ledge,  north  and  south,  the  differences  in  the  aspects  of  the  jaspers  are 
easily  recognized,  but  as  its  central  line  is  approached  the  difficulty  of 
discriminating  between  them  becomes  greater,  and  finally  in  the  middle  of 
the  ledge  it  becomes  impossible  to  distinguish  any  difference  between  them. 
There  is  certainly  no  distinguishable  unconformity  between  them  and  no 
bed  of  conglomerate  that  might  mark  an  erosion  interval.  To  all  appear- 
ances the  beds  form  a  conformable  series. 

On  the  northwest  side  of  pit  No.  3,  about  350  feet  northeast  of  the 
eastern  edge  of  the  ledge,  the  same  kind  of  flinty  jasper  is  found.  Here  it 
is  at  the  base  of  a  series  of  conformable  beds  forming  the  wall  of  the  pit. 
The  upper  layers  are  distinctly  quartzites,  containing  abundant  fragments  of 
jasper  interlaminated  with  layers  of  lean  ore,  some  of  which  apparently 
contain  large  Ijowlders  of  ore  (see  PI.  XXII,  A).  Above  the  lowermost 
distinctly  fragmental  quartzites  there  are  no  beds  of  the  cherty-looking 
jaspers.  These  are  confined  to  the  part  of  the  series  below  the  quartzite. 
The  base  of  the  series  is  not  visible,  however,  so  that  it  is  not  known 
whether  beds  containing  fragmental  jasper  occur  again  below  the  cherty 
jasper  beds  or  whether  these  latter  are  actually  beneath  the  entire  frag- 
mental series. 

CONCLUSIONS  FROM  FOREGOING  STUDY. 

It  is  clear  that  there  is  no  structural  evidence  to  indicate  that  the  jaspi- 
lites  under  consideration  are  members  of  the  Lower  Menominee  series  and 
represent  an  iron  formation  corresponding  to  the  iron-bearing  Negaunee 
formation  in  tlie  Marquette  and  Felch  Mountain  districts.  The  only 
evidence  that  bears  on  the  case  is  lithological.  The  jaspilites  are  difi'erent 
in  appearance  from  most  of  the  jaspilites  of  Upper  Menominee  age,  and  in 
their  composition  and  texture  are  similar  to  the  jaspilites  of  Negaunee  age 
in  other  districts.  So  far  as  has  been  noted  they  contain  no  fragniental 
material,  but,  on  the  other  hand,  they  seem  to  have  an  oolitic  structure. 
Since  they  are  beneath  beds  that  are  certainly  members  of  the  lowest  iron 


ALGONKIAN,  NEGAUNEE  FORMATION.  279 

formation  in  the  Upper  Menominee  series,  it  might  be  conclnded  that  they 
represent  a  small  portion  of  the  iron-bearing  Lower  Menominee  formation 
which  has  yielded  so  much  material  to  the  overlying  iron-bearing  Upper 
Menominee  formation.  There  are  other  considerations,  however,  which 
tend  to  cast  doubt  on  this  conclusion.  If  the  jaspilites  are  Negaunee  in 
age,  the  immediately  underlying  rocks  should  be  the  cherty  upper  members 
of  the  dolomite  formation.  The  absence  of  these  cherts  seems  to  demand 
the  assumption  of  an  erosion  interval  between  the  jaspilites  and  the  dolomite 
formation  of  sufficient  dui-ation  to  allow  of  the  entire  removal  of  the  cherts. 
If  this  assumption  is  a  correct  one,  it  would  necessitate  the  placing  of  the 
jaspilites  in  the  Upper  Menominee  series  with  the  Traders  member  of  the 
ViTlcan  formation.  It  is  not  certain,  however,  that  the  chert  was  ever  a 
uniform  layer  overlying  the  dolomite  and  coextensive  with  it,  in  spite  of 
the  fact  that  wherever  found  it  is  at  or  near  the  top  of  the  formation. 
Of  course,  if  it  never  existed  in  this  place  its  absence  indicates  nothing 
Avith  respect  to  the  age  of  the  jaspilites. 

It  is  almost  impossible  to  reconcile  the  absence  of  an  unconformity 
between  these  jaspilites  and  the  overlying  jaspilites  of  the  Vulcan  formation 
with  the  view  that  the  two  jaspilites  belong  to  two  different  series.  In 
many  places  it  might  be  difficult  to  recognize  such  an  unconformity,  even 
if  present,  because  of  the  fact  that  the  contact  between  the  Lower  and  the 
Upper  Menominee  series  was  a  zone  of  accommodation  along  which  the 
original  relations  between  the  beds  in  contact  were  often  obliterated  by 
shearing.  In  the  present  instance,  however,  where  the  two  jaspilites  strike 
and  dip  uniformly,  there  has  been  no  marked  disturbance  of  the  beds,  and, 
in  spite  of  this  fact,  no  evidence  of  an  unconformity  between  them  can  be 
detected.  Indeed,  the  two  varieties  of  jaspilites  grade  into  one  another 
like  the  beds  of  a  single  formation. 

In  a  word,  while  the  evidence  that  has  thus  far  been  adduced  as  bear- 
ing upon  the  age  of  the  cherty  jaspilites  is  not  entirely  conclusive,  it  seems 
to  jjoint  to  the  fact  that  they  are  parts  of  the  Traders  member  of  the  Vulcan 
formation.  They  are  recognized,  however,  as  being,  on  the  whole,  differ- 
ent lithologically  from  the  characteristic  jaspilites  of  the  Traders  member, 
although  in  the  open  pit  of  the  Quinnesec  mine  and  at  one  or  two  other 
places  in  the  district  there  are  beds  that  look  very  much  like  the  jaspilites 
considered  here.  These  beds  are  above  the  quartzite  which  contains  frag- 
ments of  jasper,  and  so  are  unquestionably  younger  than  Negaunee. 


280  THE   MENOMINEE  IRON-BEAEING  DISTRICT. 

SECTIOK  3.     ITPPER  MEXOMINEE  SERIES. 

CHARACTER  AND   OCCURRENCE. 
COMPONENT    FORMATIONS. 

The  Upper  Menominee  series  comprises  all  the  beds  between  the  top 
of  the  Randville  dolomite  and  the  bottom  of  the  Lake  Superior  sandstone. 
It  includes  two  formations  which  have  been  called  the  iron-bearing  Vulcan 
formation  and  the  Hanbury  slate.  The  former — the  lower  of  the  two — 
is  made  up  of  three  members,  which  in  the  order  of  succession  are  the 
ii'on-bearing  Traders  member,  the  Brier  slate,  and  the  iron-bearing  Curry 
member.  The  Traders  member  is  in  some  places  further  divisible  into 
a  lower  portion  consisting  mainly  of  slates  and  quartzite,  and  an  upper 
portion,  consisting  principally  of  ore  and  jasper  beds. 

SEPAKATION      FROM      THE      OVERLYING      SANDSTONE      AND      THE      UNDERLYING      LOWER 

MENOMINEE    SERIES. 

The  separation  of  the  series  from  the  overlying  Lake  Superior 
sandstone  is  necessitated  by  the  universal  presence  of  a  profound 
unconformity  between  the  two,  the  existence  of  which  is  made  evident 
not  only  by  many  visible  contacts  showing  horizontal  layers  of  sandstone 
resting  upon  the  eroded  edges  of  the  upturned  lower  rocks,  but  by  the 
presence  everywhere  of  immense  fragments  of  the  iron-formation  rocks  in 
the  basal  member  of  the  sandstone. 

The  necessity  for  the  separation  of  the  Upper  Menominee  series  from 
the  Lower  Menominee  series  is  not  very  evident  at  first  sight.  Visible 
contacts  between  the  iron-bearing  Traders  beds  and  the  Randville  dolomite 
are  rare.  In  those  instances  where  the  contacts  are  seen  the  two  formations 
appear  to  be  conformable.  The  folding  of  the  district  has  been  so  severe 
that  the  slight  discordances  in  bedding  that  may  have  once  existed  have 
been  entirely  obliterated  by  movements  of  accommodation. 

The  principal  evidence  that  is  relied  upon  as  a  basis  for  the  separation 
of  the  two  series  is  the  character  of  the  lower  layers  of  the  iron-bearing 
Traders  member  and  the  structure  of  many  of  its  ore  and  jasper  beds.  In 
many  places  immediately  over  the  dolomite,  especially  along  the  southern 
border  of  the  southern  dolomite  area,  a  distinct  and  very  definite  bed  of 
coarse  quartzite  occurs,  through  which  small  fragments  of  bright-red  jasper 


ALGONKIAN,  UPPER  MENOMINEE  SERIES.  281 

and  small  rounded  grains  of  a  l)lack  hematite  are  plentifully  sprinkled.  The 
rock  is  usually  not  so  coarse  grained  as  to  warrant  its  being  called  a  con- 
glomerate, but  it  has  the  essential  characteristics  of  the  conglomerate  at  the 
base  of  the  Ishpeming  formation  in  the  Upper  Marquette  series.  The  com- 
ponents of  the  Menominee  rock  are  not  so  large  as  those  of  the  Marquette 
rock,  nor  are  the  ore  and  jasper  fragments  so  abundant.  Nevertheless,  these 
fragments  possess  characters  as  distinctly  fragmental  as  do  those  in  the 
Marquette  conglomerate.  The  latter  has  been  employed  as  evidence  that 
the  iron  formation  underlying  the  Ishpeming  quartzite  is  of  much  greater 
age  than  the  latter,  and  therefore  that  the  Marquette  bedded  rocks  are 
divisible  into  a  lower  series  and  an  upper  series.  In  this  district  the  iron- 
bearing  Negaunee  formation  is  visible  at  many  places  beneath  the  conglom- 
erate, so  that  comparison  of  its  nature  with  that  of  the  fragments  in  the 
conglomerate  is  easy.  The  character  of  the  fragments  is  so  like  that  of 
much  of  the  material  in  the  bedded  Negaunee  rocks  that  no  doubt  can  be 
felt  as  to  their  origin.  They  were  2jlainly  derived  from  the  Negaunee  rocks 
by  wave  action  along  a  shore  line.  In  the  Menominee  district  the  coarse 
quartzite  was  also  a  shore-line  deposit,  and  its  ore  and  jasper  fragments 
must  have  been  deri^'ed  from  an  older  formation.  But  no  source  for  these 
fragments  has  yet  been  discovered.  There  is  no  iron  formation  in  the 
district  corresponding  to  the  Negaunee  formation  in  the  Marquette  district, 
nor  has  there  been  discovered  anywhere  in  the  Archean  schists  of  the  district 
any  evidence  of  the  existence  of  jaspilites  interbedded  with  the  greenstones 
similar  to  those  associated  with  the  g-reen  schists  of  the  Marquette  and  the 
Vermilion  districts.  In  the  two  districts  last  named  the  jaspilites  in  the 
Archean  have  furnished  jasper  and  a  few  ore  pebbles  to  the  conglomerates 
at  the  base  of  the  Huronian  series,  so  that  even  if  the  jaspilites  had  not 
been  observed  in  position  their  jwesence  somewhere  in  the  Archean  series 
would  have  been  inferred  from  the  presence  of  these  pebbles  in  the  lowest 
member  of  the  overlying  series.  The  basal  conglomerates  of  the  Lower 
Menominee  series  show  no  jasper  pebbles,  though  they  exhibit  specimens 
of  practically  all  the  rocks  known  to  exist  in  the  Archean.  The  plain  infer- 
ence from  these  two  facts — (1)  the  absence  of  jaspers  from  those  jDortions 
of  the  Menominee  Archean  that  have  come  under  observation,  and  (2)  the 
absence  of  jasper  pebbles  from  the  conglomerates  at  the  base  of  the 
Huronian — is  to  the  effect  that  the   source  of  the  jasper  and  ore  in  the 


282  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

coarse  quartzite  must  be  refeired  to  the  bedded  series  between  the  basal 
conglomerates  at  the  bottom  of  the  Sturgeon  quartzite  and  the  jasper- 
bearing  quartzite  near  the  base  of  the  Traders  member.  From  the 
evident  analogy  that  exists  between  the  geology  of  the  Menominee  and 
that  of  the  Marquette  districts,  we  should  expect  to  find  an  iron  formation 
above  the  Randville  dolomite.  The  fact  that  no  such  formation  exists  in 
this  place  at  the  present  time  is  easily  explained  on  the  supposition  that  it 
was  removed  by  the  same  erosion  processes  that  were  instrumental  in 
producing  the  debris  found  now  in  the  quartzite.  No  remnants  of  the 
formation  remain,  hence  it  is  plain  that  the  shore  line  must  have  transgressed 
across  the  formation,  and  at  the  time  the  quartzite  was  deposited  it  was 
against  the  dolomite.  In  the  Marquette  district  the  shore  line  was  in  the 
iron  formation  at  the  time  the  conglomerates  now  exposed  to  study  were 
formed,  hence  these  are  composed  very  largely  of  tlie  debris  of  the  iron 
formation.  In  the  Menominee  district  the  shore  line  adjacent  to  the 
deposits  now  exposed  was  not  composed  of  iron-formation  material,  hence 
comparativel}'  little  of  this  material  is  found  in  these  deposits.  The 
greater  portion  of  it  must  be  in  deposits  that  are  now  deeply  buried,  and  it 
is  possible  that  at  these  depths  remnants  of  the  orig-inal  iron  formation  may 
still  exist. 

The  constitution  of  the  Traders  member  points  to  the  same  conclu- 
sions as  those  indicated  above.  Much  of  the  material  of  this  formation 
consists  of  the  debris  of  a  more  ancient  jaspilite  formation.  The  only 
place  for  this  seems  to  be  at  the  top  of  the  Randville  dolomite.  Since  it 
does  not  exist  there  at  present,  it  must  have  been  removed  by  erosion.  The 
assumption  necessitates  the  supposition  of  a  lapse  of  time  between  the 
deposition  of  the  dolomite  and  the  deposition  of  the  overlying  iron  forma 
tions,  and  it  is  for  this  reason  that  a  line  of  division  between  an  older 
series  and  a  vounger  series  in  the  Menominee  district  is  placed  at  this 
horizon. 

Although  no  discordance  in  stratification  has  been  observed  between 
the  top  member  of  tlie  lower  series  and  the  bottom  member  of  the  upper 
series,  the  evidence  outlined  above  is  sufliciently  strong  to  warrant  the 
assumption  of  the  existence  of  a  time  interval  between  them,  and  to 
wan-ant  the  separation  of  the  bedded  rocks  between  the  unconformity  at 
the  top  of  the  Archean  and  that  at  the  bottom  of  the  Cambrian  into  a  Lower 


ALGONKIAN,  UPPER  MENOMINEE  SERIES.  283 

Menominee  series  and  an  Upper  Menominee  series,  analagous  to  the  Lower 
Marquette  and  the  Upj^er  Marqxiette  series  in  the  Marquette  district,  and  to 
corresponding  Lower  and  Upper  Huronian  series  in  the  other  iron-ore 
districts  of  the  Lake  Superior  region. 

DISTRIBUTION. 

The  rocks  of  the  Upper  Menominee  series  occupy  the  synchnal  areas 
lying  between  the  dolomite  belts  and  between  these  and  the  areas  occupied 
by  the  Quinnesec  schists  (see  PI.  IX).  To  the  east,  like  the  formations 
of  the  Lower  Menominee,  they  pass  under  the  thick  covering  of  Paleozoic 
beds  and  are  lost  to  view.  To  the  west  they  merge  together  beyond  the 
Menominee  River  and  constitute  the  surface  rocks  over  the  larger  part  of 
the  Florence  district  in  Wisconsin. 

In  the  central  portion  of  the  Menominee  district  the  Upper  Menominee 
rocks  comprise  three  belts,  two  lying  between  the  three  dolomite  belts  and 
the  third  between  the  southern  dolomite  belt  and  the  Quinnesec  schists 
along  the  Menominee  River.  East  of  Iron  Hill  the  northern  and  central 
belts  coalesce  and  the  three  belts  are  reduced  to  two.  At  about  the 
meridian  of  Lake  Antoine  the  central  belt  coalesces  with  the  southern 
portion  of  the  northern  belt,  and  the  two  extend  to  the  Menominee  River 
between  the  southern  dolomite  and  the  western  area  of  the  Quinnesec 
schists.  In  this  portion  of  the  district,  however,  three  belts  are  still 
maintained,  for  the  western  area  of  Quinnesec  schists,  extending  eastward 
from  the  Menominee  River  like  a  wedge,  splits  the  northern  Upper 
Huronian  belt  into  two  arms,  the  southern  one  coalescing  with  the  central 
belt  as  already  related  and  the  northern  one  bending  northward  and 
following  the  Lower  Huronian  rocks  into  the  Calumet  trough. 

Over  most  of  the  areas  described  as  occupied  by  these  belts  the  Upper 
Menominee  beds  can  be  traced  by  means  of  outcrops  and  test  pits,  but  in 
the  northwest  corner  of  the  district,  in  that  portion  described  as  occupied 
by  the  northern  arm  of  the  northern  belt,  the  drift  covering  is  so  thick  that 
no  outcrops  are  found.  The  presence  of  the  Upper  Menominee  sediments 
here  is  inferred  from  the  presence  of  outcrops  of  the  Sturgeon  quartzite  and 
Randville  dolomite  at  the  northern  limit  of  the  district  and  the  presence 
of  outcrops  of  the  Upper  Menominee  beds  in  the  Calumet  trough  farther 
north. 


284  THE  MENOMINEE  IRON-BEARING  DISTRICT. 


FOLDING. 


The  character  of  the  major  folding-  of  the  Upper  Menominee  series  can 
not  be  determined  by  the  observation  of  strikes  and  dips,  since  the  expo- 
snres  are  very  few  and  the  minor  folding  is  very  pronounced.  From  the 
distribution  of  the  Upper  series  with  reference  to  the  Lower  series,  however, 
it  is  clear  that  the  former  must  exist  in  three  synclines  and  two  anticlines 
with  approximately  east- west  axes  and  in  two  anticlines  and  three  synclines 
with  north-south  axes. 

A  north-south  section  across  the  center  of  the  district,  along  the  range 
line  between  R.  29  W.  and  R.  30  W.,  cuts  all  the  folds  with  east- west  axes. 
Where  the  section  crosses  the  synclines  the  surface  rocks  belong  to  the 
Upper  Menominee  beds;  where  it  cuts  the  anticlines  the  Lower  series  is 
exposed,  the  Upper  beds  having  been  removed  by  erosion  from  the  anti- 
clinal portions  of  the  folds.  A  section  along  the  central  line  of  R.  29  W. 
cuts  two  synclines  and  a  connecting  anticline,  the  top  of  which  has  like- 
wise been  eroded;  and  a  section  along  ihe  line  between  R.  30  W.  and  R. 
31  W.  again  cuts  tlu-ee  synclines  and  two  anticlines.  In  the  latter  case  one 
anticline  is  over  the  western  area  of  the  Quinnesec  schists  and  the  other 
over  the  southern  dolomite  belt. 

The  central  dolomite  belt,  as  has  already  been  explained  (see  p. 
234),  is  an  inverted  canoe-shaped  anticline  entirely  surrounded  b}^  Upper 
Menominee  sediments.  At  each  end  the  dolomite  terminates  in  plunging 
anticlines,  overlain  by  the  Upper  Menominee  beds,  which  must  therefore 
also  be  in  closely  similar  anticlines.  The  two  taken  together  constitute  a 
broad  anticline  with  an  approximately  north-south  axis.  In  the  vicinity  of 
the  Loretto  mine,  near  the  line  between  R.  28  W.  and  R.  29  W.,  is  the  axis 
of  another  north-south  anticline.  Here  the  lowermost  beds  exposed  belong 
in  the  Upper  Menominee  series,  hence,  so  far  as  the  surface  is  concerned, 
only  the  beds  of  the  Upper  series  are  involved  in  the  fold.  The  east  limb 
of  a  third  anticline  must  occur  at  the  eastern  end  of  the  western  area  of 
Quinnesec  schists,  if  these  rocks  are  older  than  Algonkian,  as  has  been 
supposed.  Its  western  limb  is  a  dozen  or  more  miles  to  the  west  in 
Wisconsin. 

The  Upper  Menominee  beds  thus  are  affected  by  two,  and  in  a  portion 
of  the  district  by  three,  closely  compressed  folds  with  axes  trending  a  little 


ALGONKIAN,  VULCAN  FORMATION.  285 

north  of  west  and  by  two  broad  and  open  folds  with  axes  trending  a  little 
east  of  north. 

The  minor  folding-  of  the  series  will  be  discussed  in  connection  with 
the  folding-  of  its  individual  formations. 

VULCAN     FORMATION. 
DISTRIBUTION. 

From  the  230sition  of  the  Vulcan  formation  immediately  upon  the 
Lower  Menominee  beds,  we  would  naturally  expect  the  distribution  of  the 
ore-bearing  formation  to  be  determined  by  the  distribution  of  the  Lower 
series,  and,  as  a  matter  of  fact,  wherever  the  Vulcan  formation  exists  it  is 
found  immediately  above  the  Randville  dolomite  of  the  Lower  Menominee 
series  and  below  the  Hanbury  slate  of  the  Upper  Menominee.  But  at  some 
places  within  the  district  where  we  would  naturally  expect  to  find  it  the 
dolomite  is  in  immediate  contact  with  the  Hanbury  slate,  or  is  separated 
from  exposures  of  the  latter  formation  by  intervals  so  narrow  as  to  show 
that  the  Vulcan  beds  are  lacking. 

The  principal  area  of  the  Vulcan  formation  extends  as  a  belt  from  900 
to  1,300  feet  wide  along  the  south  side  of  the  southern  belt  of  dolomite  for 
nearly  its  entire  extent.  The  belt  follows  the  sinuosities  of  the  southern 
border  of  the  dolomite  area  rather  closely,  but  it  is  much  wider  in  the 
reentrants  caused  by  the  pitching  synclines  of  the  dolomite  than  elsewhere. 
The  widening  of  the  formation  at  these  places  is  of  course  due  to  the  repe- 
tition of  beds  in  consequence  of  the  folding.  Along  only  one  stretch, 
about  a  mile  in  length,  is  the  iron  formation  known  to  be  absent.  This  is 
in  the  west  half  of  sec.  1  and  the  east  half  of  sec.  2,  T.  39  N.,  R,  30  W., 
where  the  Hanbury  slate  lies  against  ledges  of  the  typical  dolomite. 

On  the  north  side  of  the  southern  dolomite  belt  the  iron  formation  has 
nowhere  been  found,  nor  has  any  indication  of  its  presence  been  detected 
except  at  the  Loretto  mine  in  the  eastern  part  of  the  district.  Near  the 
dolomite  in  the  central  and  eastern  portions  of  the  belt  magnetic  lines  are 
weak  or  absent  altogether,  and  no  exposures  of  the  Vulcan  formation  have 
been  discovered  either  in  ledges  or  by  test  pits.  On  the  other  hand,  rock 
has  been  uncovered  by  test  pits  in  the  east  half  of  sec.  11,  T.  39  N.,  R.  29 
W.,  and  near  the  northwest  corner  of  sec.  10,  T.  39  N.,  R.  29  W.  In  every 
instance  the  pits  bottomed  in  slate,  which  in  sec.  11  appears  to  make  an 


286  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

eastward-extending  embayment  into  the  dolomite  north  of  the  East  Vulcan 
mines,  and  in  sec.  10  forms  a  portion  of  the  embayment  extending  westward 
into  the  dolomite  area  east  of  Norway.  In  both  cases  the  dolomite  and  the 
slate  are  so  near  together  that  there  is  no  room  between  them  for  the 
Vulcan  formation.  Elsewhere  the  country  bordering  this  portion  of  the 
dolomite  belt  is  thickly  drift  covered,  so  that  it  is  not  known  whether  it  is 
underlain  by  a  belt  of  the  iron- bearing  formation  or  not.  In  the  eastern  por- 
tion of  the  district  the  Vulcan  beds  border  the  northern  margin  of  the  belt 
from  the  Lpretto  mine  eastward  for  a  short  distance.  At  the  Loretto  mine, 
the  ore  formation  exists  in  an  eastward-pitching  syncline.  Beyond  this 
place  it  is  traced  by  a  line  of  magnetic  attractions  to  within  a  short  distance 
of  the  east  end  of  the  area  mapped,  where  the  thick  deposits  of  Paleozoic 
beds  prevent  further  tracing. 

The  second  important  8.rea  of  the  formation  is  that  in  which  the 
Traders,  the  Cuff,  the  Indiana,  and  the  Forest  mines  are  situated.  It 
stretches  for  about  5  miles  along  the  south  side  of  the  central  dolomite 
belt,  beginning  north  of  Lake  Antoine  and  ending,  so  far  as  pi'esent  infor- 
mation indicates,  somewhere  about  the  east  line  of  R.  30  W.  Beyond 
this  point  for  a  mile  and  a  half  there  are  no  outcrops  near  the  southern 
boundary  of  the  dolomite,  nor  have  any  test  pits,  so  far  as  our  present 
knowledge  goes,  uncovered  the  underlying  rock.  Moreover,  the  magnetic 
line  which  can  be  traced  as  far  east  as  the  center  of  sec.  25,  T.  40  N., 
R.  30  W.,  gradually  dies  out  at  this  point  and  can  not  be  rediscovered  to 
the  east.  We  are  therefore  ignorant  as  to  whether  or  not  the  ore-bearing 
formation  continues  through  this  interval.  At  the  east  end  of  the  dolomite 
belt,  however,  the  country  has  been  very  thoroughly  explored  and  the 
imderlying  rocks  have  been  exposed  by  pits  and  trenches.  Lean  iron- 
bearing  slates  are  so  abundant  here  that  the  locality  is  known  locally  as 
Iron  Hill,  but  the  slates  are  different  from  those  of  the  Vulcan  formation 
and  similar  to  the  lean  iron-bearing  slates  discovered  at  several  localities  in 
the  Hanbury  slate  areas.  Further,  a  diamond-drill  hole  recently  put  down 
under  the  pits  to  within  a  short  distance  of  the  dolomite  reveals  the 
existence  only  of  gray  slates  like  those  of  the  Hanbury  formation.  The 
contact  of  the  two  formations  has  not  been  reached  by  this  drill  hole  (see 
pp.  481-483),  but  the  interval  between  the  last-known  position  of  the  slate 
and  the  nearest  exposure  of  the  dolomite  is  so  naiTOw  that  there  seems 


U.  S.  GEOLOGICAL  SURVE 


MONOGRAPH   XLVI     PL.   XVIII 


ALGONKIAN,  VULCAN  FORMATION.  287 

to  be  no  room  there  for  the  Vulcan  formation.  Again,  a  hne  of  auger 
borings  has  been  carried  from  the  northernmost  exposures  of  the  Hanbury 
slate  north  across  the  swamp  which  separates  them  from  the  southernmost 
exposures  of  the  dolomite  belt  to  within  a  few  feet  of  the  base  of  a 
dolomite  cliff,  and  these  revealed  only  slate.  While  little  confidence 
should,  perhaps,  be  placed  in  the  results  of  these  borings,  the  evidence  of 
the  absence  of  the  ^^ulcan  formation  and  the  presence  of  the  Hanbury 
slate  at  this  place  seems  so  strong  that  on  the  map  the  color  of  the  latter 
formation  has  been  carried  to  the  very  edge  of  the  dolomite  area. 

On  the  north  side  of  this  same  dolomite  belt  the  iron  formation  is 
known  to  extend  for  only  a  short  distance  on  both  sides  of  the  Cuff  mine, 
in  the  southern  portion  of  sec.  22,  T.  40  N.,  R.  30  W.  To  the  east  and 
west  the  country  is  thickly  covered  by  drift  and  sandstone,  and  nothing 
has  been  learned  of  the  nature  of  the  underlying  rock. 

The  third  strij)  of  country  in  which  the  iron-bearing  beds  are  to  be 
expected  is  that  which  borders  the  northern  dolomite  belt.  Tliis  area, 
however,  is  in  the  valley  of  Pine  Creek.  The  surface  is  thickly  covered 
with  sand.  There  is  no  indication  of  the  character  of  the  underlying  rock 
anywhei'e  west  of  the  Loretto  mine  except  that  afforded  by  a  group  of  pits 
near  the  center  of  sec.  14,  T.  40  N.,  R.  30  W.,  at  the  western  extremity  of 
the  belt.  These  pits  have  shown  the  presence  of  lean  ore  associated  with 
cherts,  jaspilites,  and  black  slates.  The  cherts  are  filled  with  the  "  shots 
and  bands  "  of  ore  characteristic  of  the  cherts  in  the  Hanbury  slate,  and 
present  to  some  extent  in  the  jaspilites  of  the  Curry  member  of  the  Vulcan 
formation.  In  this  case  the  rocks  are  believed  to  belong  to  the  Curry 
horizon. 

In  the  neighborhood  of  the  Loretto  mine  (PI.  XXIII)  the  Vulcan 
formation  appears  to  occupy  the  entire  breadth  between  the  north  side  of 
the  southernmost  belt  of  dolomite  and  the  south  side  of  the  northernmost 
belt  of  this  rock.  A  short  j^ortion  of  this  distance  has  not  yet  been 
explored,  Ijut  all  that  portion  which  has  been  opened  up  by  the  Loretto 
and  Appleton  workings  reveals  the  presence  of  one  or  the  other  members 
of  the  Vulcan  formation.  Of  the  area  east  of  the  Appleton  mine  nothing 
is  known.  The  country  is  here  covered  with  thick  deposits  of  sand  and 
sandstone. 

The  other  areas  in  which  the  Vulcan  formation  may  occur  are  those 


288 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


bordering  the  Quinnesec  schists.  From  the  order  of  succession  on  the 
northern  side  of  the  Menominee  trough  one  woukl  expect  on  the  southern 
side  of  the  trougli  to  find  in  passing  north  from  the  Quinnesec  schists  of  the 
Menominee  River  the  following  formations:  (1)  The  Sturgeon  quartzite, 
(2)  the  Kandville  dolomite,  (3)  the  Vulcan  formation,  and  (4)  the  Hanbury 
slate.  As  a  matter  of  fact,  the  only  rocks  exposed  near  the  Quinnesec 
schists  are  the  Hanbury  slates.  In  several  places  east  of  the  mouth  of  the 
Sturgeon  River,  in  the  northwest  quarter  of  sec.  26,  T.  39  N.,  R.  29  W.  (see 


]  Greenstone  , 

a  (QuinnesKO  schist) 

I  Black  slate 


\0' 


Magnetic  declination 
"  dip 


Fig.  22.— Sketch  map  of  exposures  near  Sturgeon  Falls,  sec.  26,  T.  39  N.,  R.  29  W. 

map,  tig.  22),  the  slates  and  the  schists  are  only  750  feet  apart  on  the  surface, 
but  west  of  this  point  no  exposures  of  any  kind  have  been  found  north  of 
the  schists  within  the  distance  of  less  than  a  mile. 

The  direction  of  movement  of  the  glacial  drift  in  the  Menominee  area 
was  from  the  northeast  toward  the  southwest.  The  Quinnesec  schists 
occup}'  relatively  high  groujid,  and  therefore  heav}-  masses  of  drift  were 
banked  against  their  northern  borders.  This  may  be  the  explanation  of  the 
absence  of  exposures  in  this  belt.  But  the  Sturgeon  quartzite,  the  Randville 
dolomite,  and  the  Vulcan  jaspilites  are  hard,  resistant  formations,  probably 


ALGONKIAN,  VULCAN  FORMATION.  289 

much  more  resistant  than  the  Quiunesec  schists,  hence  it  is  thought  to  be 
highly  probable  that  these  formations  do  not  rest  upon  the  schists,  other- 
Mnse  they  would  likely  be  exposed  in  some  portion  of  the  belt,  especially 
on  the  banks  of  the  Menominee  River  where  it  enters  and  leaves  the  schist 
areas.  The  absence  of  the  Sturgeon  and  Randville  formations  is  easily 
explained  on  the  supposition  that  they  were  eroded  during  the  interval  that 
developed  the  unconformity  between  the  Lower  Menominee  series  and  the 
Upper  Menominee  series.  It  is  otherwise,  however,  with  the  Vulcan  forma- 
tion. This  belongs  in  the  upper  series  along  with  the  Hanbury  .slate,  and 
unconformity  can  not  be  appealed  to  for  an  explanation  of  its  absence. 

The  Vulcan  rocks  are  fully  as  resistant  as  the  quartzite  and  the  dolo- 
mite, and  when  they  exist  they  usually  occupy  elevated  areas.  The  belt 
north  of  the  Quinnesec  schists,  however,  is  a  depressed  area;  at  any  rate, 
its  sin-face  is  nowhere  above  the  average  elevation  of  the  plain  to  the  north 
which  is  known  to  be  underlain  by  Hanbmy  slates.  Moreover,  a  magnetic 
survey  of  the  belt  showed  no  evidence  of  the  presence  through  it  of  a  definite 
magnetic  line  (see  map,  PI.  XVIII,  A).  Since,  then,  tliere  is  no  evidence 
that  the  Vulcan  formation  underlies  the  belt,  while,  on  the  other  hand,  its 
topography  indicates  that  it  is  underlain  by  the  same  rocks  that  underlie  the 
surface  immediately  to  the  north,  and  since  slate  exposures  are  found  in  the 
eastern  end  of  the  belt  within  about  750  feet  of  the  schists,  it  is  believed 
that  the  conclusion  that  the  Vulcan  formation  does  not  border  the  schist 
area  is  well  substantiated. 

The  situation  is  nearly  similar  about  the  western  area  of  Quinnesec 
schists.  Only  two  exposures  are  known  within  one-half  mile  from  the  schist 
ledges.  One  of  these  is  unquestionably  an  exposure  of  Hanbury  slate.  It 
lies  on  both  sides  of  the  Menominee  River  and  in  the  bed  of  the  stream, 
forming  a  ledge  about  900  feet  long,  in  which  the  rocks  are  gray  slates  with 
a  well-marked  cleavage  dipping  high  to  the  north.  The  north  end  of  the 
exposure  on  the  Michigan  side  of  the  river  is  south  of  and  less  than  350 
feet  distant  from  the  southernmost  ledge  of  green  schists  which  are  exposed 
under  the  railroad  bridge  of  the  Florence  branch  of  the  Chicago  and  North- 
western Railway  in  sec.  13,  T.  40  N.,  R.  31  W.  The  second  exposure, 
within  less  than  one-half  mile  of  the  schists,  is  exposed  in  the  dump  of  an 
old  shaft  in  the  northwest  quarter  of  the  southwest  quarter  of  sec.  15, 
T.  40  N.,  R.  30  W.  The  distance  from  the  shaft  to  the  nearest  outcrop  of 
MON  XLVI — 04 19 


290  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

schistose  greenstone  is  about  1,000  feet.  The  rock  exposed  in  the  dump  is 
a  ferruginous  slate  that  resembles  very  closely  some  of  the  ferruginous 
slates  of  the  Hanbury  formation  (see  p.  476).  These  exposures  are  both 
on  the  southern  side  of  the  schist  area  and  are  more  than  4  miles  apart. 
Absolutely  nothing  is  known  of  the  geology  of  the  intervening  strip  of 
country.  Nor  is  anything  known  of  the  belt  of  country  bordering  this 
schist  area  on  the  north.  This  area  is  so  deeply  buried  under  sand  and 
gravel  that  we  are  not  even  certain  that  the  northern  limit  of  the  schists 
has  been  correctly  outlined. 

No  magnetic  line  was  found  after  careful  search  surrounding  the  schist 
area,  and  no  evidence  of  any  kind  was  detected  that  indicated  the  presence 
of  an  ore  formation  in  this  place  (see  PI.  XVIII,  C).  The  occurrence  of 
the  slate  ledges  on  the  banks  of  the  Menominee  within  375  feet  of  the  schist 
exposures  renders  the  probabilities  more  favorable  to  the  belief  that  the 
Quinuesec  schists  are  surrounded  by  the  Hanbury  slate  than  to  the  view 
that  they  are  surrounded  by  a  belt  of  the  Vulcan  formation.  On  the  map  the 
color  of  the  Hanbury  slate  is  made  to  cover  the  belts  bordering  the  Quin- 
nesec  schists  in  both  areas,  although  it  is  recognized  that  in  some  places  por- 
tions of  these  belts  may  be  underlain  by  small  areas  of  the  Vulcan  formation. 

From  the  foregoing  account  of  the  distribution  of  the  Vulcan  formation 
it  will  be  noticed  that  the  belts  of  iron-bearing  rocks  are  not  continuous. 
From  the  stratigraphical  position  of  the  iron-bearing  formation  one  would 
expect  it  to  occur  as  continuous  belts  surrounding  the  dolomite  anticlines, 
bordering  the  south  side  of  the  northern  dolomite  monocline  and  the  areas 
of  Quinnesec  schist.  In  several  places,  however,  it  is  seen  that  these 
relations  do  not  exist.  It  is  known  that  in  various  parts  of  the  district 
the  iron-bearing  formation  is  absent  from  the  position  it  would  naturally  be 
expected  to  occupy,  and  that  the  Hanbury  slates,  which  stratigraphically 
overlie  the  ore-bearing  strata,  are  in  immediate  contact  with  the  dolomite 
that  underlies  the  Vulcan  formation.  Furthermore,  at  least  at  one  place  it 
is  known  that  the  slates  are  exposed  in  natural  ledges  at  so  short  a  distance 
from  the  western  area  of  Quinnesec  schists  that  there  would  seem  to  be  no 
possibility  of  the  occurrence  of  the  iron-beaHng  formation  between  them. 
It  is  probable  that  the  larger  parts  of  these  belts,  in  which  the  nnderlying 
rock  is  nnknown,  are  underlain  by  the  Hanbury  slate  rather  than  the 
Vulcan  formation,  but  it  is  possible  that  the  Vulcan  formation  underlies 
portions  of  them. 


ALGONKIAN,  VULCAN  FORMATION.  291 

TOPOGRAPHY. 

The  Vulcan  formation  is  so  thin  that,  although  in  its  usual  form  it  is 
very  resistant  to  denuding  agencies,  it  has  produced  but  little  effect  upon 
the  topography  of  the  district.  Where  the  formation  is  well  developed  it 
usually  forms  the  slopes  of  higher  ridges  of  dolomite.  Where  not  so  well 
developed,  its  topography,  except  in  a  few  instances,  gives  no  evidence  of 
its  existence  beneath.  Its  ledges  generally  present  smooth,  flat  surfaces 
that  rise  very  slightl}^  above  the  surrounding  country.  At  the  Traders 
mine  and  in  Hughitt  Bluff,  east  of  Iron  Mountain,  however,  they  form 
marked  elevations  that  can  be  seen  for  long  distances.  Because  of  the 
uniformity  in  hardness  of  the  different  components  of  the  formation  and  the 
lack  of  prominent  joint  cracks  through  it,  differential  erosion  of  its  parts  is 
not  noticeable,  and  rough  craggy  ledges,  such  as  those  characterizing  the 
resistant  dolomite  formation,  are  absent. 

SUBDIVISION  INTO  MEMBERS. 

The  Vulcan  formation  consists  of  three  distinct  parts,  that  may  easily 
be  recognized  throughout  a  large  portion  of  the  extent  of  the  formation. 
Where  only  one  of  these  parts  is  present  it  is  believed  that  it  is  always  the 
uppermost  one.  On  the  general  map  of  the  district  the  formation  is  not 
differentiated  in  the  mapping,  but  on  the  special,  large-scale  maps,  the 
formation  is  separated  into  its  parts  where  the  limits  of  these  are  known. 
The  lowermost  of  the  divisions  is  composed  of  slates,  conglomerates,  quartz- 
ites,  jaspilites,  and  ore  deposits.  It  has  been  called  the  Traders  member 
because  of  the  typical  occurrence  of  its  ferruginous  phases  at  the  Traders 
mine,  north  of  Lake  Antoine.  The  second  or  intermediate  division  com- 
prises a  belt  of  black  ferruginous  slate.  It  is  known  as  the  Brier  slate 
because  it  is  so  well  exhibited  at  Brier  Hill,  east  of  Norway.  The  third  or 
uppermost  portion  consists  of  interbedded  ferruginous  quartzites,  jaspilites, 
and  ores.  These  are  worked  for  ore  at  the  Curry  mine,  east  of  Norway, 
hence  they  have  been  named  the  Curry  member. 

TRADERS   MEMBER. 
BISTEIBCTION. 

In  spite  of  the  fact  that  the  Traders  member  is  better  developed  than 
either  of  the  other  two  members  of  the  Vulcan  formation,  where  all  are 
exposed,  nevertheless  it  seems  probable,  at  present,  that  its  distribution  is 


292  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

not  coextensive  with  that  of  the  iron-bearing  formation.  In  some  portions 
of  the  district  only  one  iron-bearing  member  appears  to  exist  and  this,  so 
far  as  the  evidence  now  at  hand  indicates,  is  the  Curry  member. 

The  Traders  member  has  been  identified  only  along  the  south  sides  of 
the  central  and  the  southern  dolomite  belts,  except  at  the  Cuff  mine,  where 
the  iron-bearing  beds  are  either  north  of  the  dolomite  or  folded  within  it, 
and  at  the  east  end  of  the  district,  where  the  Traders  beds  occur  at  the 
Loretto  and  Appleton  mines  in  the  syncline  between  the  south  side  of  the 
northern  dolomite  belt  and  the  north  side  of  the  southern  belt.  The  identity 
of  the  iron-bearing  member  at  this  place  is  established  by  the  occurrence 
above  it  of  uneroded  remnants  of  a  slate  with  the  lithological  characters  of 
the  Brier  slate.  In  the  western  portion  of  the  district  a  few  pits  have 
exposed  iron-bearing  rocks  in  sec.  14,  T.  40  N.,  R.  30  W.,  but  for  reasons 
to  be  referred  to  later  (p.  331)  these  rocks  are  believed  to  belong  in  the 
Curry  member.  Between  them  and  the  nearest  exposures  of  dolomite  to 
the  north  there  is  apparently  abundant  room  for  the  occurrence  of  the 
Traders  member  with  its  average  thickness,  but  the  interval  is  covered,  and 
the  nature  of  the  underlying  rocks  is  unknown.  Nowhere  else  along  the 
south  side  of  the  northern  dolomite  belt  are  iron- bearing  beds  known  to 
occur,  except,  as  before  mentioned,  in  the  vicinity  of  the  Loretto  and 
Appleton  mines. 

On  the  south  side  of  the  central  dolomite  belt  the  Traders  rocks  are 
found  at  the  Traders,  the  Cornell,  the  Cuff,  the  Indiana,  and  the  Forest 
mines.  At  the  two  mines  first  named  the  iron-bearing  rocks  have  the 
general  characteristics  of  the  Traders  rocks  elsewhere.  They  are, 
moreover,  overlain  by  slates  like  the  Brier  slates  at  the  type  locality.  Brier 
Hill,  and  are  sheared  and  brecciated  like  the  unquestionable  Traders  beds 
at  their  contact  with  the  underlying  dolomite.  None  of  this  rock,  however, 
has  yet  been  discovered  in  the  neighborhood  of  these  mines.  At  the  Cuff 
mine,  farther  east,  dolomite  is  on  the  south  of  the  ore-bearing  beds,  and  it 
is  reported  that  diamond-drill  holes  encountered  the  same  rock  beneath 
sandstone  to  the  north.  The  Cufif  deposits,  which  rest  directly  upon  the 
dolomite,  are  identified  as  belonging  in  the  Traders  member  by  their 
position  and  their  character.  In  all  essential  respects  they  are  similar  to 
the  beds  at  the  Traders  and  Indiana  mines.  The  ores  are  in  part  sheared 
into  specular  varieties  and  in  part  are  brecciated.     In  the  neighborhood  of 


ALGONKIAN,  VULCAN  FORMATION.  293 

the  Indiana  mine,  which  is  south  of  the  dolomite,  the  presence  of  all  three 
members  of  the  formation  has  been  disclosed  by  drilling.  The  lowermost 
member — that  one  in  which  the  shaft  was  sunk — lies  between  the  dolomite 
and  a  set  of  ferruginous  siliceous  .slates  which  are  identified  as  Brier.  This 
member  is  therefore  in  tlie  stratigraphical  position  of  the  Traders  member. 
East  and  west  of  the  Indiana  mine  a  strong  magnetic  line  and  the  rock  pile 
of  an  occasional  test  pit  shows  the  presence  of  the  iron  formation  on 
the  southern  side  of  the  dolomite  belt  between  Lakes  Antoine  and  Fumee, 
but  whether  the  ore-bearing  beds  belong  in  the  Traders  or  tlie  Curry 
member  is  not  known.  It  seems  probable,  however,  from  the  character  of 
the  rocks  on  the  dumps  of  the  pits  that  the  Traders  member  is  present,  at 
least  for  a  portion  of  the  distance  between  the  Indiana  mine  and  Lake 
Antoine,  and  it  is  probable  that  the  Indiana  beds  extend  continuously  as 
far  east  as  the  Forest  mine.  At  this  locality  the  explorations  have  developed 
two  iron-bearing  members  separated  by  a  slate.  The  northerly  one,  lying 
immediately  above  a  dolomite,  must  be  Traders.  Beyond  the  Forest  mine 
to  the  east  the  entire  Vulcan  formation  disappears  and  consequently,  ot 
course,  the  Traders  member. 

South  of  the  southern  dolomite  belt  the  Traders  member  is  well  exposed 
in  ledges,  pits,  and  mine  workings  at  many  different  points  between  Wauce- 
dah  and  the  Aragon  mine  in  sec.  9,  T.  39  N.,  R.  29  W.  Through  most 
of  this  distance  all  three  members  of  the  iron  formation  have  been  identi- 
fied, the  Traders  member  being  well  developed  throughout  nearly  its 
whole  extent.  Indeed,  practically  all  of  the  working  inines  of  this  stretch 
of  country  are  mining  Traders  ore.  Between  the  west  line  of  sec.  22,  T. 
39  N.,  R.  28  W.,  and  the  Sturgeon  River,  a  distance  of  about  3^  miles,  there 
is  no  direct  evidence  of  the  presence  of  the  Traders  member,  but  since  the 
iron  formation  is  developed  with  all  of  its  members  both  at  the  east  and 
the  west  ends  of  this  belt,  and  since  a  distinct  magnetic  line  shows  that 
the  formation  extends  through  this  distance,  the  probable  view  is  that  it 
continues  from  east  to  west  with  all  of  its  members.  From  the  Aragon  mine 
westward  to  the  center  of  sec.  1,  T.  39  N.,  R.  30  W.,  where  the  entire  for- 
mation disappears,  the  iron  formation  is  well  exposed  by  test-pitting  and 
mining  operations.  At  the  Norway  and  Cyclops  mines  the  Traders  and  the 
Curry  members  are  both  developed.  West  of  these  mines,  in  sec.  6,  T.  39 
N.,  R.  29  W.,  however,  only  one  iron-bearing  member  is  exposed.     No 


294  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Brier  slate  is  recognized  as  being  associated  with  the  jaspihtes,  but,  on  the 
other  hand,  these  rocks  appear  to  be  bordered  on  the  south  by  the  slates 
of  the  Hanbury  formation.      The  Traders  member,  therefore,  appears  to  be 
generally  absent  from  this  belt  of  country.    At  any  rate,  it  has  not  yet  been 
>shown  to  be  present.     One  or  two  drill  holes  put  down  in  this  region  are, 
however,  reported  to  have  penetrated  a  series  of  slates  lying  between  a 
considerable  thickness   of  iron-bearing  beds  and  a  thin  series  of  similar 
heds,    the  latter    being  against  the    dolomite.     Portions    of   the    Traders 
member  may  therefore   exist  at  a  little   depth  beneath  the   surface;   but 
immediately  at  the  surface  there  is   no  indication  of  the  presence  of  the 
member  between  the  Norway  mine  and  Quinnesec.     From  the  Quinnesec 
mine    westward  about  a    mile    there    are    three    belts    of   iron   formation 
material  separated  by  Brier  slates.     The  belt  between  the  northernmost 
slate   belt    and    the    dolomite    is  unquestionably   a    part    of  the    Traders 
member,  and  it  is  believed  that  the  belt  to  the  south  of  this  is  also  Traders. 
On  this    supposition    the    Traders    member   in    the    Quinnesec    syncline 
borders  the  north  and  east  sides  of  the  basin  and  forms  a  narrow  anticlinal 
tono^ue  extending  three-fourths   of   a    mile    westward  through  its   center. 
To  the  east  the  Traders  member  disappears  in  sec.  2,  T.  39  N.,  R.  30  W., 
■with  the  entire  Vulcan  formation,  and  to  the  west  it  is  believed  to  thin 
<out  in  the  southwest  quarter  of  sec.  34,  T.  40  N.,  R.  30  W.,  to  reappear 
.again  at  the  Pewabic,  Walpole,  Millie,  and  Chapin  mines  as  a  narrow  belt 
.bordering  the  dolomite  and  following  it  in  all  its  complicated  folding.     At 
the  anticlines  the  iron-bearing  member  extends   westward    much  farther 
than  the  dolomite,  producing  several  belts  bounded  on  both  sides  by  Brier 
slates  (see  map,  PI.  XXVIII,  for  details).     Beyond  the  old  Ludington  mine 
in  the  southeast  quarter  of  sec.  25,  T.  40  N.,  R.  31  W.,  the  Traders  member 
seems  again  to  disappear,  the  most  westerly  point  at  which  its  rocks  can 
be  identified  being  on  the  dump  heaps  of  the  old  Ludington  shafts. 

While  the  Traders  member  is  not  as  continuous  as  the  Curry  member, 
nearly  all  the  mines  of  the  district  have  obtained  their  ores  from  its 
deposits,  so  that  a  map  of  the  active  and  abandoned  mine  shafts  would 
.serve  to  show  the  approximate  distribution  of  the  member. 

LITHOLOGT. 

The  Traders  member  consists  of  a  conformable  set  of  beds  composed 
of  thin  layers  of  light-colored  shaly  slates,  heavily  ferruginous  quartzose 


ALGONKIAN,  VULCAN  FORMATION.  295 

slates,  ferruginous  conglomerates,  ferruginous  quartzites,  jaspilites,  and 
iron-ore  deposits.  On  the  sections  of  mine  workings  these  are  designated 
the  Traders  slate,  Traders  quartzite,  and  Traders  ore-bearing  beds. 

SLATES. 

Macroscopical. — The  slates  of  the  Traders  member  are  commonly 
either  light-colored  argillaceous  phases  that  may  contain  considerable  talc, 
or  dark-gray  sandy  hematitic  slates  that  differ  from  the  fragmental  ores 
mainly  in  containing  too  little  hematite  to  be  profitably  mined.  These 
slates  are  usually  at  the  base  of  the  Traders  member,  although  in  some 
places  thin  layers  of  the  lighter-colored  slates  are  interbedded  with  con- 
glomerates and  quartzites  a  short  distance  above  the  base.  The  relations 
between  the  argillaceous  and  the  ferruginous  slates  have  not  been  observed, 
as  the  two  phases  have  not  been  found  together.  The  latter  seem  to  be 
more  locally  developed  than  the  former,  which  appear  to  be  almost  univer- 
sally present  between  the  Randville  dolomite  and  the  adjacent  iron-bearing 
formation.  Some  of  the  slates  that  are  described  in  preceding  pages  as 
occurring  at  the  top  of  the  Randville  dolomite  may  belong  here.  These 
are  almost  identical  in  character  with  the  slates  of  the  Vulcan  formation 
and  are  not  separable  from  the  latter  upon  structural  grounds.  Where 
represented  on  the  maps  in  this  volume  the  argillaceous  slates  are  denomi, 
nated  "The  Traders  slate."  The  ferruginous  slates,  which  are  more  closely 
related  to  the  iron-bearing  deposits  than  to  the  true  slates,  are  distinguished 
as  the  "Traders  ferruginous  slates."  They  are  separated  from  the 
remainder  of  the  hematite  beds  mainly  for  economic  reasons.  On  the 
mine  plats  the  argillaceous  slates  are  frequently  mapped  as  "talcose 
slates."  From  the  fact  that  they  are  always  found  in  juxtaposition  with 
the  dolomite,  and,  in  appearance  resemble  very  closely  the  slates  that  are 
interbedded  with  the  dolomite  beds,  they  are  popularly  spoken  of  in  the 
district  as  "marble  slates." 

The  argillaceous  slates  vary  from  dark  purple  to  white,  through  various 
shades  of  red  or  yellow.  Originally,  perhaps,  nearly  all  were  white  or  light 
yellow,  for  in  most  cases  the  darker  color  is  plainly  due  to  staining  by  iron 
oxides.  Nearly  all  phases  are  dull  in  luster  and  thus  are  usually  easily 
distinguished  from  certain  white  leached  slates  of  the  Hanbury  formation, 
which  are  highly  sericitic.  Here  and  there,  however,  where  slipping  has 
taken  place  parallel  to  the  bedding,  sllckensides  have  been  produced,  and 


296  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

along  the  slipping  surfaces  taleose  or  micaceous  minerals  have  developed. 
On  such  surfaces  the  slates  are,  of  course,  lustrous;  but  a  fracture  across 
the  bedding  layers  will  usually  show  surfaces  that  are  dull  and  earthy. 

In  many  places  the  slates  may  be  seen  to  grade  into  tine-grained 
quartzites  through  the  increase  in  the  proportion  of  quartz  present  and  the 
diminution  of  the  clayey  constituents.  On  the  other  hand,  the  gradation 
is  sometimes  accomplished  through  the  alternation  of  thin  slate  and  quartzite 
layers,  the  latter  increasing  in  number  and  thickness  until  the  former 
entirely  disappear. 

In  some  localities  the  slates  are  much  sheared,  usually  along  their  bed- 
ding planes,  but  sometimes  transversely.  In  these  phases  the  slaty  cleavage 
is  well  developed.  Most  specimens  exhibit  no  cleavage,  but  split  easily 
along  the  bedding  planes  between  the  layers  into  thin  shaly  fragments. 
Movements  of  accommodation  occurred  here.  The  layers  readjusted  them- 
selves to  the  new  stresses  produced  by  folding  and  slipped  over  one  another, 
as  is  to  be  expected  of  thin  slate  beds  between  two  resistant  rocks  like  the 
dolomite  and  the  jaspilite.  Where  the  folding  was  sharp  the  movements  of 
readjustment  were  greater  than  elsewhere  and  the  slates  were  more  intensely 
sheared.  The  resulting  rock,  with  its  cleavage  surfaces  often  covered  with 
a  coating  of  talc,  kaolin,  or  other  micaceous  mineral,  like  the  taleose  schists 
already  referred  to,  furnished  nearly  impervious  linings  to  many  of  the 
synclines  in  the  underlying  dolomite  and  thus  provided  suitable  troughs  for 
the  concentration  of  the  ores. 

The  argillaceous  or  taleose  slates,  as  has  already  been  observed,  are 
found  at  or  near  the  base  of  the  Traders  member,  often  interleaved  with 
the  coarse  quartzites  or  fine-grained  conglomerates  to  be  described  later. 
Where  the  quartzites  and  conglomerates  are  abundant  the  slate  beds  are 
apt  to  be  thin  and  few;  where  the  quartzose  deposits  are  few  and  thin  the 
slates  are  thick.  Usually  there  is  a  distinct  band  of  slate  between  the 
lowermost  conglomerate  bed  and  the  neighboring  dolomite,  though  it  may 
not  be  more  than  a  foot  thick.  At  first  this  was  thought  to  be  evidence  that 
the  slates  under  discussion  always  belong  in  the  dolomite  series  with  the 
conglomerates  at  the  base  of  the  Vulcan  formation.  Since,  however,  beds 
of  slate  identical  with  those  immediately  above  the  dolomite  are  now  known 
to  occur  between  conglomerate  beds,  it  is  believed  that  many  of  these  slates 
are  members  of  the  Vulcan  formation.     Their  character  would    indicate 


ALGONKIAN,  VULCAN  FORMATION.  297 

deep-sea  conditions  at  tlie  beginning  of  Upper  Huronian  time.  This 
conclusion  is  also  suggested  by  the  fact  that  no  coarse  basal  conglomerates 
were  laid  down  at  the  base  of  the  Vulcan  formation  such  as  were  deposited 
at  the  base  of  the  Ishpeming  formation  in  the  Marquette  district.  When  we 
consider  tliat  the  deposits  derived  from  the  hard  jasper  of  the  Lower 
Huronian,  which,  in  shallow  water  along  shores,  would  naturally  contain 
large  bowlders  of  this  excessively  hard  substance,  consist  of  quartzites  con- 
taining but  a  few  small  pebbles  of  jasper,  the  inference  that  the  water  was 
comparatively  deep  at  the  places  where  the  deposits  now  occur  seems  to  be 
fairly  warranted.  If  this  inference  is  correct,  we  have  a  ready  explanation 
of  the  lack  of  apparent  discordance  between  the  Lower  Huronian  and  the 
Upper  Huronian  deposits,  for  it  is  only  close  to  shore  lines  that  discordance 
between  formations  is  to  be  expected. 

The  ferruginous  slates  are  dark-blue  or  dark-gray,  heavy,  sandy- 
looking  rocks  that  sparkle  with  reflections  from  the  faces  of  innumerable 
little  hematite  crystals  that  are  scattered  uniformly  through  their  masses. 
These  slates  grade  into  lean  ores,  from  which  they  differ  merely  in  per 
cent  of  hematite  present.  They  occur  at  only  a  few  places,  notably  at  the 
Traders  mine,  where  they  can  be  plainly  seen  on  the  east  side  of  the  large 
open  pit. 

Microscopical  and  chemical. — The  argillaceous  slates  of  the  Traders 
member  are,  for  the  most  part,  confused  aggregates  of  small  kaolin  spicules, 
larger  ones  of  a  greenish  muscovite,  and  a  few  of  greenisli-brown  biotite, 
a  few  flakes  of  light-colored  chlorite,  many  sharp-edged  grains  of  quartz, 
enlarged  here  and  there  by  the  addition  of  quartz  material,  and  numerous 
small  I'ound  masses  of  limonite  and  irregular  accumulations  of  magnetite, 
all  lying  in  a  matrix  composed  of  quartz  grains  with  indefinite  outlines  and 
a  few  masses  of  cloudy  material  stained  red  by  hematite  and  limonite  dust. 
The  cloudy  material  may  be  decomposed  feldspars.  Here  and  there, 
scattered  through  this  aggregate,  are  long  columnar  masses  of  limonite, 
which  look  as  though  they  might  be  the  alteration  products  of  biotite  or 
hornblende,  and  small  needle-like  crystals  of  zircon.  In  some  places  these 
components  are  arranged  in  such  a  manner  as  to  suggest  that  they  may 
have  been  derived  from  a  fairly  coarse-grained  fragmental  rock,  but  in  the 
greater  part  of  the  sections  no  original  structure  is  discernible.  It  is 
evident  that  most  of  the  present  constituents  are  secondary  and  that  the 


298 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


rock  has  been  subjected  to  silicificatiou  processes.  Kaolin  is  by  far  the 
most  abundant  component  after  quartz.  Its  proportion  with  respect  to  the 
latter  varies  in  different  sjjecimens,  but  in  all  specimens  both  these  constit- 
uents predominate  largely  over  all  others.  In  a  few  specimens  there  are 
no  other  minerals  present  except  the  small  grains  of  limonite  and  an 
occasional  mica  flake. 

An  analysis  of  a  purplish-pink  slate  from  the  dump  of  an  old  shaft 
near  the  center  of  sec.  5,  T.  39  N  ,  R.  29  W.,  about  on  the  contact  of  the 
Traders  formation  and  the  Raudville  dolomite  north  of  the  Norway  mine, 
gave  Mr.  E.  T.  Allen,  of  the  Survey  laboratory,  the  result  exhibited  below 
in  Column  I.     The  corresponding  molecular  ratios  are  printed  in  italic. 


Analyses  of  slates  of  Traders  membei\ 

I. 

II. 

III. 

SiOj   

67.04 
1.119 
15.01 

.m 

3.  .54 
.0'22 

3.18 
■  044 

2.11 
.OSS 
.19 
.003 
.29 
.005 

4.00 
.043 
.67 

3.73 
.S07 
.69 
.009 
.03 
.02 
Tr. 
Tr. 
Tr. 

67.76 

14.12 

.81 

4.71 

2.38 

.63 

1.39 

3.52 

.23 
2.98 

.71 

.07 

(FeS,)=     .22 

(00^)=     .40 

.10 

.04 

47.85 

AlA „.... 

18.13 

FcO, .... 

6.14 

FeO 

.10 

MgO 

14.51 

CaO 

Tr. 

Na^O 

.21 

K2O              

2.91 

H2Oatl05° 

HjO  above  105° 

09.  96 

TiO, - - 

P,0, 

S 

CrA 

MnO 

BaO 

Total 

100. 50 

100.07 

99.81 

a  Loss  on  ijemltioii. 


ALCtONKIAN,  VULCAN  FORMATION.  299 

In  column  III  is  the  analysis  of  a  purple  fissile  slate  from  beneath 
(north  of)  the  ore  on  the  fifth  level  of  the  Chapin  mine.  Between  the 
laminae  are  slickensided  surfaces  covered  with  talc.  The  analysis  was 
made  by  Mr.  E.  E.  Brewster,  chemist  of  the  Pewabic  mine,  to  whom  great 
obligations  are  acknowledged  for  the  favor  of  publishing  this  and  other 
analyses  furnished  by  him.  In  column  II  is  quoted  an  analysis  of  a  sea- 
green  roofing  slate  from  West  Pawlet,  Vt."  The  analyses  show  clearly  that 
the  argillaceous  phases  of  the  Traders  slates  are  composed  largely  of  the 
debris  of  granitic  rocks,  such  as  those  forming  the  northern  area  of  the 
Archean.  The  high  magnesian  content  of  the  rock  from  the  Chapin  mine  is 
plainly  due  to  the  presence  of  the  talc  which  infiltrated  along  the  fissile 
planes  in  solutions  emanating  from  the  dolomite. 

The  mineral  composition  of  the  first  slate  calculated  from  its  analysis 
in  Column  I  is  approximately  47  per  cent  quartz,  20  per  cent  kaolin,  5^  per 
cent  muscovite,  8.8  per  cent  orthoclase,  6  per  cent  penninite,  and  2J  per 
cent  limonite. 

The  quartzose  phases  of  the  slates  diff'er  but  little  from  the  argillaceous 
phases  just  described.  In  these  much  of  the  quartz  is  in  round  or  oval 
grains  that  are  usually  homogeneous.  Sometimes  the  original  grains  are 
broken  up  into  mosaics  of  small  grains,  the  outlines  of  the  mosaic  aggre- 
gates corresponding  to  the  outlines  of  the  original  grains.  Nearly  all  the 
grains  are  crossed  by  strain  shadows.  The  matrix  in  which  these  are 
embedded  difi"ers  little  in  its  character  from  that  of  the  argillaceous  slates. 
Quartz  and  kaolin  constitute  its  principal  con.stituents.  Sometimes  this  is 
traversed  by  irregular  streaks  rich  in  small  flakes  of  brown  biotite,  and 
scattered  indiscriminately  througli  it  ai"e  occasional  large  wisps  of  muscovite 
or  sericite.  The  usual  limonite  grains  and  some  hematite  particles  are  also 
present. 

The  ferruginous  slates  differ  markedly  from  the  argillaceous  and 
quartzose  phases  described  above.  They  consist  of  nearly  equal  parts  of 
opaque  hematite  in  individual  crj'stals  and  groups  of  crystals  and  a  color- 
less matrix  composed  of  small  clastic  quartz  grains,  wisps  of  muscovite, 
cloudy  masses  of  some  decomposed  feldspar,  a  little  light-green  chlorite, 
and  a  considerable  quantity  of  crystallized  quartz   cementing  the   other 

oBuU.  U.  S.  Geol.  Survey  No.  168,  1900,  p   278;  also  Nineteenth  Ann.  Rept.  U.  S.  Geol.  Survev, 
pt.  3,  1899,  pp.  232  and  243. 


300  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

components.  The  hematite  is  the  most  noticeable  constituent.  Its  groups 
sometimes  consist  of  a  very  few  grains  aggregated  in  an  irreguhir  manner, 
and  at  other  times  they  comprise  a  great  number  of  grains  united  in  such  a 
way  as  to  form  aggregates  that  are  much  longer  in  one  direction  than  in 
any  other.  There  is  thus  produced  a  slight  schistosity  in  the  rock,  which 
is  accentuated  to  some  degree  by  the  tendency  of  the  muscovite  to  arrange 
itself  in  a  direction  parallel  to  the  elongation  of  the  hematite  groups.  These 
slates,  like  the  argillaceous  phases,  are  mechanical  sediments.  They,  how- 
ever, have  had  deposited  in  them  a  gi-eat  quantity  of  hematite  and  much 
silica.  Thus  they  are,  in  a  way,  intermediate  forms  between  the  argilla- 
ceous slates  and  the  jaspilites. 

CONGLOMERATES   AND   QUARTZITES. 

Macroscopical. — The  conglomerates  and  quartzites  are  usually  at  or 
near  the  base  of  the  member,  in  some  places  resting  immediately  upon 
the  Randville  dolomite,  and  at  other  places  sepai'ated  from  the  dolomite 
by  one  or  more  beds  of  the  shaly  slates  just  described.  They  vary  in 
thickness  from  a  few  inches  to  20  feet  or  more.  They  contain  fragmerits, 
usually  small  but  occasionally  large,  of  quartzite,  jasper,  colorless  and  white 
quartz,  and  rocks  that  make  up  the  Archean  complex. 

The  more  massive  phases  have  the  appearance  of  coarse,  dark-colored 
quartzites  composed  of  fi-agments  of  the  above-mentioned  rocks,  usually 
varying  in  size  from  4  to  10  millimeters,  lying  in  a  dark-purple  or  brown 
groundmass  made  up  of  small,  colorless,  brilliantly  glistening  quartz  grains 
in  what  appears  to  be  a  homogeneous  matrix  of  a  dark  color  and  a  dull 
luster.  In  this  rock  bands  filled  with  large  fi-agments  alternate  with  others 
free  from  them.  Further,  some  of  the  foi'mer  contain  an  abundance  of 
sharp-edged  pieces  of  jasper,  while  others  contain  none.  Much  of  the  rock 
is  more  or  less  schistose,  but  never  is  it  as  schistose  as  the  more  ferruginous 
phases  described  below.  With  increasing  schistosity  the  quartz  and  other 
fragments  become  more  and  more  elongated  and  the  jasper  fragments  are 
rotated  to  a  position  parallel  to  the  schistosity. 

In  many  cases  the  conglomerate  contains  so  much  hematite  and  jasper 
that  it  is  an  ore-and-jasper  conglomerate  or  quartzite.  In  these  instances 
the  ore  and  jasper  are  sometimes  in  fragments  embedded  in  a  quartzitic 
matrix  like  that  above  described,  but  more  usually  the  ore  is  in  small  grains 
scattered    through   the   matrix  in  which    larger  fragments  of  jasper    are 


ALGONKIAN,  VULCAN  FORMATION.  301 

embedded.  Often  the  hematite  constitutes  such  a  hirge  portion  of  this 
matrix  that  to  all  appearances  it  is  a  comparatively  pure  ore. 

These  varieties  are  nearly  always  strongly  schistose.  On  the  cleavage 
surfaces  of  the  less  schistose  phases  the  oi-e  fragments  a})pear  as  little 
shining  oval  plates  up  to  8  mm.  in  length  and  little  sln-eds  from  1  to 
6  mm.  long.  The  jasper  fragments  are  smaller  and  sometimes  have  angular 
outlines,  but  usually  these,  too,  are  oval  in  shape.  They  are  often  of  the 
same  dark-purple  color  as  the  matrix  in  which  they  are  embedded,  and  so 
are  difficult  to  distinguish.  On  surfaces  that  lie  across  the  schistosity  the 
ore  particles  appear  simply  as  lines  parallel  to  the  schistose  stnicture,  while 
the  jasper  pai'ticles  are  much  elongated  ovals. 

Typical  occurrences  of  the  quartzose ,  phases  of  these  conglomerates 
and  coarse  quartzites  are  found  near  the  base  of  the  Vulcan  series  in  the 
open  pit  of  the  Quinnesec  mine  and  in  the  ledges  bordering  the  south  side 
of  the  little  valley  at  the  Brier  Hill  mine.  They  occur  also  in  similar 
positions  in  many  of  the  mines,  and  fine  specimens  may  be  found  on  their 
dump  heaps.  The  ferruginous  types  are  especially  abmidant  at  the  Traders, 
the  Cuff,  the  Millie,  and  the  Pewabic  mines  and  in  many  of  the  exploring 
pits  north  of  the  Cui'ry  and  West  Vulcan  mines. 

As  the  quantity  of  hematite  in  the  quartzite  increases,  the  rock  tends 
to  lose  its  fragmental  character  and  to  assume  a  schistose  structure.  The 
ore  aiid  jaspilite  fragments  are  mashed  into  lenticiilar  bodies,  and  the  matrix 
into  a  mass  of  thin  scales  like  those  characterizing  the  specular  ores  of  the 
Marquette  district. 

When  in  this  form  the  rocks  are  typical  jaspilites.  These  are  well 
represented  in  the  exposures  forming  Hughitt  Bluff,  east  of  Iron  Mountain. 
Here  the  jasper-bearing  quartzose  layers  have  given  rise  to  purple-mottled 
jaspers  and  the  ferruginous  layers  have  yielded  specular  ore  bands.  All 
gradations  are  represented  at  this  place  between  rocks  that  still  retain 
evident  clastic  characteristics  and  those  in  which  no  trace  of  fragmental 
material  remains.  The  finer  the  original  grain  of  these  rocks  and  the  more 
schistose  their  present  structure  the  more  homogeneous  are  the  resulting 
bands  and  the  more  difficult  is  it  to  distinguish  in  them  any  distinct  evi- 
dence of  their  original  clastic  character.  At  the  west  end  of  Hughitt  Bluff 
the  original  sediments  were  fairly  coarse;  hence  the  rocks,  although  very 
schistose,  still  yield  proofs  that  they  were  originally  fragmental.     In  the 


302 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


most  fragmental  phases  the  distinction  between  quai'tzose  and  ferruginous 
layers  is  not  marked.  The  former  are  hghter  colored  than  the  latter,  a 
little  more  siliceous,  and  a  little  more  granular.  The  latter,  on  the  other 
hand,  contain  more  hematite  and  are  therefore  more  schistose  and  less 
granular. 

In  some  localities,  more  particularly  at  the  Traders  and  Cuff  mines, 
the  conglomerates,  together  with  the  banded  ores  and  jaspers,  have  become 
brecciated  through  mashing,  so  that  the  most  apparent  structure  is  the 
brecciated  one.  Long,  fiat,  lenticules  of  jasper  and  ore  are  interwoven  in 
such  a  manner  as  to  give  the  rock  the  appearance  of  a  conglomerate.     At 

first  sight  this  pseudo-conglomeratic  struc- 
ture mav  be  taken  for  a  true  cong'lomer- 
atic  structure,  but  a  careful  examination 
of  the  ledges  will  show  that  there  is  a 
definite  and  regular  alternation  of  jasper 
lenses  with  ore  lenses  in  such  a  manner 
as  can  be  explained  only  on  the  supposi- 
tion that  they  represent  the  shattered 
portions  of  what  were  originally  continu- 
ous bands  of  quartzose  and  ferruginous 
materials.  Moreover,  the  rocks  are 
strongly  schistose,  with  the  schist  planes 

Fig.  23. — Sketch  of  contortions  in  jasper  bands,  west  ,  .•  ,i         i  i         .t       n  i  ttti 

side  of  ciifTord  pit,  illustrating  production  of  cuttuig  the   bauds  at  all  augles.      Where 

breccias,      n,     Jasper;     b,     schisto.se     hematite,    .i  \  •    ±       'j.        ■       1  •     1,1         •       T         1     j.       j.i 

Dotted  lines  show  direction  af  schistosity.    Area  the    SClnStOSlty    IS    highly    mclmed    tO    the 

<igured,about5by3feet.  banding  the  jaspcr  bands   are   dissected 

by  occasional  cracks  and  their  dissevered  portions  are  rotated  into  positions 
tending  to  conform  with  the  schistosity  (see  fig.  23).  Thus  the  individual 
bands  may  be  made  up  of  large  numbers  of  lenses  with  their  longer  axes 
lying  athwart  the  direction  of  the  bands,  but  parallel  to  the  direction  of 
the  schistosity.  Their  ends  frequently  fit  the  ends  of  the  next  adjacent 
lenses.  The  true  conglomeratic  structure  of  the  rock  is  recognized  only 
upon  very  close  inspection  of  some  of  the  jasper  lenses.  These,  when 
examined  carefully,  are  seen  to  be  composed  of  fragments  of  jasper  inclosed 
in  a  fine-grained  matrix  of  jasper,  sand,  and  hematite  flakes.  Under  the 
microscope  the  fragmental  character  of  all  the  jasper  bands  is  quite  plain. 
Microscopical. — Most  of  the  coarse  quartzites  or  fine-grained  conglom- 


ALGONKIAN,  VULCAN  FORMATION.  303 

erates  at  and  near  the  base  of  the  Traders  member  are  composed  of  large 
rounded  grains  of  quartz  and  small  pebbles  of  the  same  mineral,  often 
enlarged  by  the  addition  of  quartz  material  in  optical  continuity  with  the 
surrounded  nucleus,  and  elongated  sharp-edged  or  subangular  fragments  of 
jasper  lying  in  a  groundmass  consisting  essentially  of  quartz  and  hematite 
(see  PI.  XIX,  A,  E).  The  quartz  is  in  small  polygonal  grains,  interlocking 
with  one  another  to  form  a  mosaic  in  which  the  hematite  and  other  rarer 
components  of  the  groundmass  are  embedded.  No  indications  of  the 
presence  of  clastic  quartz  can  anywhere  be  detected  in  this  mosaic.  The 
quai'tz  must  have  formed  in  situ,  replacing  completely  the  original  cement 
by  which  the  pebbles  and  large  quartz  grains  were  united.  The  hematite 
usually  occurs  in  two  distinct  forms,  but  occasionally  a  third  form  is 
observed.  The  greater  portion  of  the  mineral  is  in  irregular-shaped, 
angular  masses  that  are  apparently  aggregates  of  small  crystals.  Another, 
but  much  smaller  portion,  is  in  large,  well-developed  crystals  scattered  here 
and  there  irregularly  through  the  quartz  mosaic.  Occasionally  one  of 
these  crystals  is  half  within  a  large  quartz  grain,  the  other  half  projecting 
outward  into  the  quartz  mosaic.  The  third  form  is  in  little  curved  streaks, 
outlining  oval  areas  or  forming  a  ring  or  several  concentric  rings  surround- 
ing areas  constituted  exactly  like  the  mosaic  of  the  groundmass.  These, 
for  reasons  that  will  be  given  later  (see  p.  344),  are  believed  to  be  pseudo- 
morphs  of  concretions  in  a  ferruginous  sediment.  Their  presence  indicates 
that  the  groundmass  of  the  conglomerates  contained  originally  a  considerable 
quantity  of  a  chemically  deposited  ferruginous  carbonate  or  silicate  which 
was  later  rej^laced  by  silica  and  hematite.  Further,  the  entire  quartzose 
groundmass  is  dotted  with  a  dust  of  tiny  grains  of  transparent  hematite. 

In  those  beds  in  which  the  proportion  of  liematite  present  is  very 
great,  the  hematite,  in  addition  to  the  forms  described  above,  occurs  also 
as  occasional  fragments  intermingled  with  the  enlarged  quartz  grains. 
Here  and  there  through  the  crystalline  quartz  matrix  are  also  little  rounded 
jasper  grains  that  are  peripherally  enriched  by  concentric  bands  of  ore, 
and  ramifying  between  the  quartz  and  ore  fragments  are  small  stringers  of 
very  dense  hematite,  which  looks  as  though  it  were  infiltrated  in  the  form 
of  veinlets  after  the  rock  had  become  silicified.  Scattered  throug-h  the 
matrix  a  few  wisps  of  biotite  are  sometimes  observed  in  the  sections  and 
occasionally  there  is  present  a  shred  of  muscovite,  but  usually  the  only 
constituents  of  the  rocks  are  quartz  and  hematite. 


304  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

In  the  few  localities  where  the  formation  is  not  much  disturbed,  as, 
for  instance,  near  the  center  of  the  northeast  quarter  of  sec.  9,  T.  39  N., 
R.  29  W.,  where  the  flat  lying  Traders  member  is  overlain  by  the  Lake 
Superior  sandstone,  the  fragmental  charactei-  of  the  rock  is  very  apparent. 
Here  the  ore  and  the  jasper  are  in  distinctly  angular  pieces  and  the  matrix 
is  a  well-defined  quartzite  made  up  of  enlarged  quartz  grains.  This  matrix, 
however,  passes  gradually  into  a  finer-grained  matrix  composed  of  inter- 
locking grains  in  which  no  distinction  between  nucleal  and  added  quartz 
can  be  made  out.  The  fragmental  grains  seem  to  have  been  replaced  in 
parts  of  the  sections  by  secondary  material. 

Usually  the  only  evidences  of  the  clastic  nature  of  these  rocks  is  the 
presence  in  them  of  the  abundant  rounded  quartz  grains  and  of  a  few  jasper 
and  ore  fragments.  Moreover,  this  evidence  is  often  obscure,  for  nearly  all 
the  beds  except  the  coarsest  ones  exhibit  schistosity,  and  this  structure,  even 
in  its  less  marked  stages,  is  peculiarly  effective  in  obliterating  the  frag- 
mental character  of  the  constituents,  especially  in  those  cases  in  which  a 
considerable  portion  of  these  consist  of  ore  grains.  When  the  quartzites  are 
interbedded  with  layers  very  rich  in  hematite  the  latter  are  always  nn;ch 
more  schistose  than  the  former,  often  resembling  in  appearance  the  typical 
specular  ores  of  the  Marquette  district.  Where  this  is  the  case  all  evidences 
of  the  presence  of  ore  fragments  in  these  bands  have  disappeared,  though 
the  fragmental  origin  of  much  of  the  material  in  the  quartzitic  bands  inter- 
bedded with  those  bands  may  still  be  apparent.  When  the  quartzitic  layers 
become  sheared  these  too  lose  their  clastic  structure.  The  smaller  quartz 
pebbles  and  the  jasper  fragments  break  up  into  mosaics  aiid  the  ore  pebbles 
are  drawn  out  into  long  narrow  streaks.  In  this  manner  beds  of  interlami- 
nated  quartzite  and  hematite  pass  into  well-characterized  jaspilites  that  are 
sometimes  indistinguisliable  from  those  derived  from  chemical  sediments. 

Thus  the  whole  aspect  of  the  quartzites  and  fine-grained  conglomerates 
is  that  of  a  sediment  composed  of  many  coarse  ore  and  jasper  fragments 
and  fine  quartz  sand,  which  has  been  thoroughly  silicified  by  the  deposition 
of  silica  between  the  larger  grains  and  the  entire  replacement  of  the 
cementing  matei'ial  by  this  substance.  In  one  or  two  instances  that  have 
been  observed  it  has  seemed  probable  that  the  replaced  cement  was  mainly 
fragmental  quartz  sand  which  had  been  almost  completely  dissolved  and 
redeposited  before  the  rocks  became  schistose,  but  in  most  instances  no 


ALGONKIAN,  VULCAN  FORMATION.  305 

such  process  is  indicated.  The  structure  of  the  mosaic  is  identical  with 
that  of  the  jaspers,  and  it  may  well  be  that  in  the  ^^resent  case,  as  in  the 
case  of  the  jaspers  to  be  discussed  later,  the  silica  has  replaced  a  ferrugi- 
nous carbonate  or  a  silicate.  If  this  is  so  the  original  deposits  were  com- 
posed of  a  mixture  of  chemically  deposited  substances  and  detritus  from 
an  older  jasper  and  ore  formation.  At  the  very  base  of  the  formation  the 
detrital  portion  was  in  great  excess  and  the  resulting  rocks  were  mainly 
coarse  quartzite  and  fine-grained  conglomerates.  Interstratified  with  these 
at  little  higher  horizons,  beds  of  almost  pure  jasper  now  occur,  and  these 
were  originally  beds  of  chemically  deposited  carbonate  and  silicate  with  no 
admixture  of  fragraental  material.  The  mottled  jaspers  described  above 
must  have  been  composed  of  ferruginous  compounds  containing  more  or 
less  abundant  sand  grains  and  small  pebbles. 

Although  the  quartzites  and  conglomerates  have  been  subjected  to 
deformation  stresses  usually  sufficiently  intense  to  cause  mashing  of  the 
smaller  quartz  pebbles,  nevertheless,  in  only  a  few  instances  have  these 
caused  any  evident  crushing  of  the  larger  pebbles  or  the  production  of 
strain  shadows  in  them.  In  the  conglomerate  bed  at  the  base  of  the  ore 
formation  in  the  open  pit  of  the  Quinnesec  mine,  however,  the  effects  of 
pressure  are  very  marked.  In  the  hand  specimen  the  rock  is  like  the 
coarse  quartzites  elsewhere,  with  the  exception  that  it  is  distinctly  schis- 
tose. In  thin  section  the  small  pebbles,  when  revolved  between  crossed 
nicols,  are  seen  to  be  crossed  by  strain  shadows  which  are  differently 
oriented  in  different  jjortions  of  the  same  pebble.  In  the  interior  of  the 
grains  the  areas  characterized  by  the  different  shadows  are  physically  con- 
tinuous. Near  their  peripheries,  however,  minute  cracks  develop  between 
neighboring  areas.  These  widen,  and,  at  the  border^  of  many  of  the  grains, 
partigles  become  entirely  separated  from  the  main  portion  of  the  grain, 
forming  a  granulated  zone  around  it.  With  the  separation  of  these  parts 
the  stresses  in  them  seem  to  be  relieved  somewhat,  for  many  of  the  dissev- 
ered particles  are  free  from  strain  shadows  while  the  neighboring  portions 
of  the  unbroken  grain  exhibit  them  in  great  perfection.  This  process  of 
granulation  has  proceeded  so  far,  especially  in  the  case  of  the  fragments 
that  were  originally  sharp  edged,  that  the  entire  area  of  the  original  grain 
is  now  a  mosaic  of  little  grains,  each  of  which  is  divided  by  tiny  cracks 
into  several  portions,  all  of  which,  however,  are  crossed  by  a  uniform 
MON  xLvi — 04 20 


306  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

shadow.  Often  these  granulated  masses  retain  the  outline  of  the  original 
fragment,  but  usually  they  are  drawn  out  into  long  narrow  strings  or  very 
flat  cm'ved  lenses  which  strongly  accentuate  the  schistosity  of  the  ground- 
mass.  This  latter  is  made  up  of  large  and  small,  apparently  fragmental, 
quartz  grains  free  from  strain  shadows,  occupying  areas  of  various  elongated 
shapes  and  interspersed  with  these  are  streaks  of  interlocking  quartzes 
forming  well-defined  mosaics.  The  quartzes  in  the  mosaics  are  filled  with 
the  usual  hematite  dust,  while  those  in  the  fragmental  aggregate  contain 
practically  no  inclusions.  About  a  third  of  the  rock  consists  of  hematite. 
This  is  present  in  dense,  opaque  lines  that  run  nearly  parallel  to  the  schis- 
tosity, in  long  lenticular  streaks  of  massive  ore,  and  in  comparatively  large 
isolated  crystals  within  the  quartz  matrix  and  sometimes  lying  partly  within 
this  and  partly  within  the  areas  of  the  granulated  masses  supposed  to  result 
from  the  crushing  of  quartz  pebbles.  The  dense,  massive  ore  appears  to  fill 
narrow  crevices  opened  up  in  the  rock  parallel  to  its  structure.  The  crys- 
tals were  formed  after  the  material  of  the  rock  was  deposited,  but  before  it 
was  completely  silicified  and  made  schistose.  The  ore  streaks,  the  lines  of 
hematite  crystals,  and  the  long  narrow  lenses  of  the  crushed  quartz  flowed 
around  the  large  pebble-like  quartz  areas  in  a  way  known  only  in  rocks  of 
clastic  origin  that  have  been  made  schistose  by  pi'essure. 

The  rock  of  the  Traders  mine  presents  some  peculiarities  that  warrant 
at  least  a  brief  special  mention.  In  the  ledge  the  rock  is  apparently,  as  has 
been  stated,  a  sheared  conglomerate  or  breccia  composed  of  large  jasper-like 
pebbles  in  a  matrix  of  specular  ore.  Under  the  microscope  the  apparent 
pebbles  are  themselves  seen  to  be  made  up  of  fragments  from  some  older 
jasper  bed,  and  the  rock,  as  a  whole,  is  discovered  to  be  a  brecciated 
series  of  fragmental  beds.  The  ore  matrix  presents  no  unusual  features. 
It  is  an  aggregate  of  crystals,  streaks,  and  flattened  masses  of  hematite 
inclosing  numerous  grains  of  quartz.  The  appearance  of  the  jasper  sections 
is  strikingly  like  that  of  many  tuff's.  In  natural  light,  under  low  powers, 
they  exhibit  the  usual  features  of  individual  and  grouped  crystals  of  hematite 
lymgm  a  colorless  matrix  of  quartz  containing  numerous  siuall  red  inclusions. 
Under  medium  powers,  however,  the  nature  of  the  inclusions  is  seen  to  be 
quite  difl'erent  from  that  of  the  inclusions  of  the  more  normal  jaspers. 
Without  exception,  they  are  the  fragments  of  a  colorless  substance,  that 
seems  to  be  quartz,  filled  with  very  fine,  red  dust  that  resembles  earthy 


ALGONKIAN,  VLTLCAN  FORMATION.  307 

hematite.  The  fragments  vary  in  their  largest  dimensions  from  0  03 
to  0.06  mm.,  and  are  extremely  variable  in  shape.  Some  are  rod-like, 
others  rounded,  and  yet  others  irregular  in  outline  with  sharp  corners.  The 
majority,  however,  are  in  general  triangular  or  quadrangular,  with  curved 
bounding  surfaces.  In  other  words,  these  fragments  have  the  same  shapes 
as  the  glass  splinters  in  many  volcanic  ashes.  If  present  in  a  rock  of 
another  character  than  this,  they  might  be  cited  as  evidence  of  its  volcanic 
origin.  In  the  present  instance  there  can  be  no  doubt  that  the  rock  is  a 
sediment.  The  fi-agmeuts  are  probably  fine  splinters  forcibly  broken 
from  a  jasper,  which,  like  all  rocks  with  a  conchoidal  fracture,  yielded 
flakes  with  curved  surfaces.  The  fragments  lie  in  all  positions  within -and 
between  the  grains  of  the  quartz  mosaic,  the  linear  dimensions  of  which  are 
from  three  to  four  times  as  great  as  those  of  the  fragments.  A  few  sericite 
shreds  occur  here  and  there  between  the  quartz  grains,  otherwise  the  mosaic 
is  like  that  in  all  the  other  jasj^ers  of  this  district. 

The  rock  was  probably  originally  composed  of  small,  sharp-edged 
fragments  of  jasper  and  round  ore  fragments  in  a  matrix  that  was 
subsequently  silicified. 

JA8PILITES. 

Macroscopical. — With  increasing  distance  from  the  base  of  the  formation 
the  conglomerates  and  quartzites  pass  upward  into  cherty  or  jasper-like 
rocks,  the  former  gray  and  the  latter  dai-k  red  or  purple  in  color.  The 
gray  cherty  rocks  are  exceedingly  rare  in  the  Traders  member,  being  found 
at  only  a  very  few  places  in  the  formation  and  at  these  places  in  subordinate, 
amount. 

These  siliceous  rocks  occur  in  layers  that  vary  in  thickness  from  a 
fraction  of  an  inch  to  18  inches  or  2  feet.  They  are  always  inter- 
laminated  with  hematite  layers,  forming  the  banded  rock  known  as  jaspilite. 
Some  of  them  on  fresh  fractures  exhibit  the  quartzitic  textiire  very  plainly. 
The  coarser  of  them  approach  ferruginous  quartzites.  Others,  however, 
resemble  very  closely  a  typical  jasper,  which  in  some  cases  they  are 
believed  to  be.  The  former  are  often  mottled  by  red  and  purple  blotches 
that  appear  to  be  due  to  the  presence  of  red  jasper  grains  in  a  ferruginous 
quartzose  matrix.  In  the  greater  number  of  instances  the  mottling  is  in  small 
elongated    areas  and  the    rock    possesses    an    incipient    schistosity  in  the. 


308  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

direction  of  tlie  longer  axes  of  the  areas.  This  phenomenon  is  the  result 
of  mashing,  which  flattened  the  jasper  grains  and  the  smaller  components 
of  the  quartzose  matrix,  producing  a  parallel  arrangement  of  the  particles. 
It  is  diflicult  to  determine  with  certainty  the  relative  amounts  of  the  detrital 
material  and  true  jasper"  (secondarily  deposited)  present,  but  apparently 
the  former  is  the  more  abundant  in  many  specimens,  and  it  may  predom- 
inate in  most.  In  a  few  instances  the  structure  of  the  siliceous  layers  is 
clearly  fragmental.  This  is  beautifully  shown  in  a  specimen  obtained  from 
the  north  end  of  a  trench  crossing  the  iron  formation  just  east  of  the  Cuff 
mine.  The  rock  has  a  reddish-purple  color.  Through  a  purple  jasper 
grouttdmass  are  scattered  a  great  many  small,  irregular-shaped,  brilliant- 
red  jasper  fragments  with  sharp  edges.  Because  the  rock  is  not  sheared 
the  fragments  are  easily  recognized.  Such  a  rock,  if  made  schistose  by 
mashing  and  shearing,  would  no  doubt  give  rise  to  a  mottled  variety, 
like  the  mottled  jaspers  refei'red  to  in  the  preceding  paragraph.  A  second 
type  of  fragmental  texture  is  well  exhibited  by  some  of  the  siliceous  bands 
in  pit  No.  2,  north  of  the  Curry  mine.  The  dark-purple  jasper  is  dotted 
with  little  irregular  grains  of  a  gray  hematite  lying  in  all  possible  positions 
within  the  bands.  These  ai-e  plainly  fragmental.  Together  with  a  consid- 
erable number  of  small  jasper  fragments  they  constitute  large  portions  of 
the  rocks.  In  places  the  ore  particles  become  larger  and  more  numerous, 
jnerging  into  well-defined  bands.     At  the  same  time  the  structure  becomes 

oin  this  discussion  the  term  "jasper"  is  applied  to  the  nonfragmental  aggregate  of  cherty 
quartz  and  hematite  flakes  associated  with  the  hematite  layers  in  the  iron  formations.  The  term 
"  jaspilite"  is  applied  to  the  banded  rock  composed  of  alternating  layers  of  jasper  and  hematite.  It 
is  true  that  the  latter  term  was  first  proposed  by  Wadsworth  to  designate  the  jaspers,  on  the  assump- 
jtion  that  the  jasper  associated  with  the  Marquette  rocks  is  an  eruptive  rock  "more  acid  than  the 
rhyolites."  (Notes  on  the  geology  of  the  iron  and  copper  districts  of  Lake  Superior:  Bull.  Mus.  Comp. 
:  Zoology,  vol.  7,  1880,  p.  76.)  But  when  it  was  shown  that  the  jaspers  are  sedimentary  in  origin  the 
employment  of  the  term  in  Wadsworth's  sense  was  no  longer  applicable.  V'an  Hise  then  suggested 
that  the  term  be  retained  as  a  convenient  one  to  designate  the  "rocks  consisting  of  alternating  bands 
composed  mainly  of  finely  crystalline,  iron-stained  quartz  and  iron  oxide."  {Mon.  U.  S.  Geol. 
;Survey,  vol.  28,  p.  362.)  In  this  sense  the  tenn  is  used  as  a  convenient  descriptive  one  in  this  volume. 
In  the  preliminary  report  on  the  Menominee  district  (Geologic  Atlas  U.  S.,  folio  62,  U.  S.  Geol. 
Survey,  p.  4)  the  discrimination  between  the  terms  jasper  and  jaspilite  was  not  always  made,  nor  in 
the  monograph  in  which  the  term  "jaspilite"  was  redefined  was  this  term  always  used  in  the  newly 
defined  sense  (cf. :  "The  hard-ore  jasper  or  jaspilite,"  a  few  lines  above  the  definition  quoted  above). 
In  the  present  monograph  all  the  siliceous  material  in  the  iron  formation  which  is  now  composed 
entirely  or  largely  of  interlocking  quartz  grains  (whether  originally  clastic  or  not)  will  be  calleil 
jasper,  and  rocks  composed  of  alternating  bands  of  jasper  and  hematite  will  be  designated  jaspilites. 


ALGONKIAN,  VULCAN  FORMATION.  309 

dense  and  the  individuality  of  the  constituent  grains  is  lost.  Even  without 
the  aid  of  the  microscope  it  is  clear  that  there  has  been  a  secondary- 
deposition  of  ore  material  between  the  fragments,  welding  them  into  a 
homogeneous  mass. 

These  distinctly  fragmental  types  grade  into  the  mottled  jaspers,  which 
are  sheared  j^hases  of  the  same  rock,  and  these  in  turn  pass  gradually  by 
the  loss  of  their  mottlings  into  the  aphanitic,  flinty  jaspers  with  a  wax-like 
luster. 

The  ferruginous  layers  associated  with  the  conglomerates  and  the 
quartzites  become  more  numerous  as  the  latter  grade  into  jaspers,  and  the 
alternations  of  the  siliceous  and  ferruginous  materials  beco^ie  more  regular. 
These  associated  iron  oxides  usually  occur  in  beds  no  thicker  than  the 
quartzose  layers.  At  various  places,  however,  especially  in  the  basins  pro- 
duced by  the  folding  of  the  dolomites,  they  rapidly  thicken  and  replace 
the  quartzose  layers  along  their  strike,  forming  ore  deposits,  which  may  be 
sufficiently  large  to  waiTant  mining. 

The  thin-bedded  ores  are  usually  gray  specular  varieties,  strongly 
resembling  in  appearance  the  Marquette  specular  ores  from  the  Ishpeming 
formation.  The  readjustments  due  to  folding  occurred  mainly  in  the  soft 
ferruginous  bands  between  the  harder  siliceous  ores,  and  as  a  result  the 
former  have  been  sheared  and  the  hematite  rendered  micaceous.  In  some 
cases  the  shearing  was  so  severe  that  it  affected  the  jasper  and  ore  alike  and 
both  became  schistose.  On  fractured  surfaces  along  the  schistose  planes  of 
the  ores,  especially  when  these  surfaces  have  been  slightly  weathered,  there 
is  noticeable  a  peculiar  texture  that  possesses  considerable  significance.  On 
such  surfaces  a  distinction  can  be  made  out  between  a  fine-grained  matrix 
and  numerous  comparatively  large  oval  or  lenticular  areas.  The  latter  give 
uniform  reflection  from  their  entire  surfaces,  while  the  matrix  reflects  from 
many  small  surfaces.  The  appearance  thus  produced  is  that  of  a  number 
of  large  flattened  grains  in  a  groundmass  composed  of  small  grains.  This 
texture  is  characteristic  of  fragmental  sediments.  Considered  in  connection 
with  the  fact  that  ore  fragments  are  known  to  be  present  in  some  of  the 
jaspers  (cf ,  p.  308),  the  texture  is  regarded  as  indicating  that  many  of  the 
ore  layers  are  composed  largely  of  fragmental  material. 

The  ore  bands  interstratified  with  the  siliceous  ones  are  not  always 
schistose,  nor  have  they  always  the  mottled  appearance  of  the  typically 


310  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

fragmental  ores.  In  many  cases  the  interbeclded  ore  is  a  dense  black 
variety,  almost  aphanitic  in  texture,  but  striped  parallel  to  the  bedding  with 
narrow  lines  that  look  like  lines  of  sedimentation.  The  ore  of  this  kind  is 
mainly  secondary,  having  been  deposited  along  the  planes  between  contig- 
uous jasper  layers  or  along  bedding  cracks  that  may  have  been  opened 
within  original  fen-uginous  layers.  In  these  cases  there  is  usually  a  sharp 
contact  line  between  the  ferruginous  and  the  siliceous  layers,  and  the  bor- 
ders of  the  former  are  often  denser  and  harder  than  their  interior  portions, 
which  are  composed  principally  of  original  material.  In  the  case  of  the 
bands  that  consist  largely  of  granular  or  micaceous  hematite,  the  transition 
from  these  layers  to  the  siliceous  ones  is  more  frequently  gi-adual.  The 
jasper  near  the  ore  is  highly  charged  with  hematite.  Moreover,  near  the 
borders  of  the  bands  naiTow  seams  of  the  siliceous  material  are  interlam- 
inated  with  the  broader  ferruginous  ones.  These  become  more  numerous 
and  broader,  predominating  over  the  ore  bands  and  finally  exceeding  them 
altogether.  In  many  instances  ore  bands  that  at  first  sight  look  homoge- 
neous are  found  iipon  close  inspection  to  be  made  up  throughout  of  minute 
interlaminations  of  hematite  and  jasper.  J 

Like  all  other  fragmental  sediments,  the  ores  contain  a  variable  quan- 
tity of  impui'ities.  Much  of  this  impurity  consists  of  quartz  grains  and  of 
the  constituents  that  are  usually  found  in  slates.  Sometimes  the  proportion 
of  such  substances  is  so  great  that  the  ores  are  not  marketable.  They  are 
then  known  as  slates.  The  blue  or  dark-gray  slates  occurring  under  the 
ore  at  the  Clifford  pit  of  the  Traders  mine  and  in  the  dump  heaps  of 
the  Cuff  and  Indiana  mines  are  of  this  character.  They  are  fen-ugin- 
ous sediments  in  which  the  proportion  of  ore  grains  is  not  sufficiently 
great  to  warrant  working.  On  their  cleavage  surfaces  these  slates  look  like 
fine-grained  specular  ores,  but  on  cross  fractures  they  have  a  dull  luster 
and  are  marked  by  obscure  bands  due  to  sedimentation.  Moreover,  they 
have  a  distinct  argillaceous  odor  and  are  noticeably  lighter  in  weight  than 
the  merchantable  ores.  With  a  lens  the  constituents  can  easily  be  made 
out  to  be  ore  particles  and  grains  of  a  dull  yellowish-white  mineral. 

The  distinction  between  ore  and  slate  at  the  Traders  mine  is  mainly 
based  on  economic  considerations.  The  boundary  line  between  the  two 
oscillates  with  the  demands  of  the  ore  market.  At  the  present  writing, 
however,  those  deposits  in  which  the  impurities  are  distinctly  visible  as 


ALGONKIAN,  VULCAN  FORMATION. 


311 


yellowish-white  grains  disseminated  through  the  mass  are  unmarketable. 
The  marketable  ores  are  confined  to  those  in  which  the  impurities  are 
jasper  fragments  or  secondary  silica  aggregated  into  narrow  bands.  The 
guaranteed  quality  of  the  Traders  ore  is:  Fe!=41.00  per  cent,  P  =  .020  per 
cent.     Cargo  analyses  of  the  ore  shipped  in  1899  averaged  as  follows  : 

Average  analysis  of  ore  from  Traders  mvne. 

Fe 41.  01 

SiOj 39. 10 

P - 014 

Mn 


S  .... 
CaO. 


.09 
.003 
.97 
.49 


MgO 29 

HjO  above  105° 2. 55 

The  surface  surrounding  the  mine  has  been  exhaustively  test-pitted 
and  the  contents  of  the  pits  have  been  carefully  tested  for  iron  and 
phosphorus.  The  results  of  these  analyses  exhibit  well  the  gradual 
transition  between  ore  and  slate.  The  numbers  are  those  given  to  the 
different  pits  on  the  mine  plats.  Of  these  the  first  four  pits  are  regarded  as 
in  slate,  the  balance  as  in  ore.  The  arbitrary  division  between  slate  and 
ore  is  at  35  per  cent  Fe. 

Iron  content  of  rock  taken  from  test  pits  north  of  the  Clifford  open  pit. 


No.  6. 

No.  3. 

No.  12. 

No.  1. 

No.  7. 

No.  13. 

No.  11. 

No.  8. 

No.  9. 

Fe 

29.70 
.011 

31.50 
.008 

33.  019 

33.30 
.011 

35.10 
.011 

39.10 
.040 

44.20 
.009 

45.  30 
.008 

49.40 

P 

.022 

The  rocks  constituted  by  the  alternations  of  the  siliceous  and 
ferruginous  bands  often  resemble  very  closely  the  jaspilites  of  the 
Marquette  district.  The  brilliant  red  banding  of  the  Marquette  rock  is, 
however,  noticed  at  only  a  few  places  in  the  Menominee  district.  The 
prevailing  color  of  the  Menominee  jaspers  is  dark  purple  or  brown. 
In  a  few  instances,  especially  where  the  siliceous  bands  contain  very 
little  fragmental  jasper,  the  red  color  may  be  marked,  as  in  the  case 
of  some  of  the  bands  in  the  Quinnesec  open  pit  and  in  the  ledge  north- 
west of  the  Curry  shaft  No.  2,   which  has   already  been   refeiTed  to  as 


312  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

illustrating  the  character  of  the  jaspiUtes  of  the  Negaunee  formatiou 
(p.  275).  On  the  weathered  surfaces  the  siHceous  bands  frequently  take 
on  a  deep-red  color,  and  on  the  surfaces  of  joint  cracks  druses  of  brilliant- 
red  quartz  crystals  often  cover  the  ends  of  the  bands,  but  the  color  in 
both  instances  is  only  superfcial.  It  rarely  penetrates  the  rock  to  any 
great  depth. 

In  most  cases,  except  where  the  rock  is  brecciated,  the  bauds  are  con- 
tinuous, with  a  uniform  thickness  for  long  distances.  Occasionally  the 
bands  wedge  out,  and  when  this  occurs  it  is  without  exception  the  siliceous 
ones  that  so  disappear,  the  fen-uginous  ones  wrapping  ai'ound  their  ends  and 
coalescing.  The  result  of  this  is  the  appearance  of  lenticular  masses  of  jasper 
embedded  in  schistose  ore  (see  PI.  XX,  B).  Sometimes  the  lenses  are  small 
and  numerous,  measuring  one-fourth  or  one-half  inch  in  their  long  diameters; 
sometimes  the  dissevered  masses  are  spherical  rather  than  lenticular.  In 
both  cases  the  resulting  schist  is  knotty,  resembling  in  general  appearance 
micaceous  schists  that  are  studded  with  staurolite  or  garnet  crystals.  Well- 
marked  phases  of  lenticular  and  brecciated  jaspers  are  to  be  seen  in  the 
rock  piles  of  the  Traders  and  the  Cuff  mines  and  in  the  pits  lying  along 
the  contact  of  the  Vulcan  formation  and  the  Randville  dolomite  and 
stretching  from  the  Norway  mine  to  the  West  Vulcan  mine  These  all 
exhibit  the  structure  on  a  large  scale.  They  are  plainly  nearly  all 
brecciated  jaspilites.  At  other  places,  notably  west  of  Iron  Mountain,  the 
typical  lenses  occur,  and  these,  so  far  as  can  be  learned,  are  not  connected 
with  brecciation. 

Where  folded  the  siliceous  bands  are  often  crossed  by  cracks  and 
fissures,  on  the  walls  of  which  are  druses  of  quartz  or  calcite  and  hematite 
crystals.  Veins  of  quartz,  of  calcite,  and  of  dense  hematite  also  traverse 
the  ore  and  jasper  bauds  indifferently,  and  not  infrequently  hematite  veins 
are  intercalated  in  the  ore  bands  parallel  to  their  bedding.  The  vein  ore  is 
always  denser  and  more  granular  than  the  surrounding  ore,  and  from  the 
fact  that  the  vein  material  often  lacks  schistosity  when  the  intruded  ore  is 
schistose  it  follows  that  the  former  must  have  been  deposited  after  the 
period  of  readjustment,  during  which  folding  occurred. 

Where  the  rocks  are  folded  the  ore  bands  usually  thicken  and  the  ores 
take  on  a  character  very  different  from  that  of  the  ore  in  the  thin  beds. 
They  lose   then-  specular  habit   and   their  steel-gray  color   and   become 


ALGONKIAN,  VULCAN  FORMATION.  313 

granular  in  texture  and  dark  blue  or  black  in  color.  This  change  is 
noticed  to  occur  particularly  at  the  ends  and  in  the  troughs  of  folds  and  in 
places  where  the  rocks  have  been  crushed  or  jointed.  In  these  places  the 
water  that  is  constantly  circulating  through  the  rocks  has  removed  silica 
and  deposited  hematite  (see  pp.  352,  395),  thus  producing  the  ore  deposits  of 
the  district.  New  hematite  has  built  out  the  plates  of  the  original  ore  into 
grains.  At  the  same  time  it  has  filled  or  partly  filled  with  ore  the  openings 
that  were  produced  during  the  crushing  and  jointing  of  the  rock.  Where 
the  crushing  was  considerable  the  ore  may  present  a  porous  aspect  and  all 
joint  cracks  may  be  lined  with  druses  of  hematite  cr3'stals.  In  other 
instances  the  thickening  of  the  ore  beds  is,  in  part  at  least,  an  original 
efi"ect  and  not  one  due  to  secondary  causes.  Some  places  along  the 
original  shore  lines  were  more  favorably  situated  for  the  accumulation 
of  the  ferruginous  sediments  than  others.  Here  the  deposits  settled  in 
greater  abundance  than  elsewhere  and  made  thick  beds.  The  ore  bodies 
thus  produced  may  pass  gradually  along  the  strike  into  ferruginous  jaspers, 
whereas  when  the  change  is  due  to  secondary  enrichment  the  passage  may 
be  comparatively  sudden.  The  ore  deposits  are  thus  exceedingly  variable 
in  thickness,  in  some  places  measuring  only  a  few  inches,  in  others  reaching 
200  feet  or  more. 

Microscopical. — When  viewed  under  the  microscope  the  jaspilites  are 
found  to  be  in  most  instances  thoroughly  crystalline.  Even  those  speci- 
mens which  in  the  hand  specimen  show  a  distinct  mottling  exhibit,  only 
in  a  few  cases,  a  fragmental  structure  when  studied  in  thin  sections.  Those 
which  exhibit  this  structure  best  are  the  jaspilites  of  Hughitt  Bluff. 

Sections  of  these  rocks  show  both  ore  and  jasper  fragments  in  a 
matrix  resembling  that  of  the  homogeneous  jaspers  described  in  succeeding 
pages.  The  ore  fragments  consist  of  long  oval  or  lenticular  masses  of  a 
very  fine  aggregate  of  quartz  grains  and  tiny  hematite  flakes.  Streaks  of 
a  coarse-grained  and  dense  ore  penetrate  these  masses  in  a  direction 
parallel  to  their  long  axes,  and  usually  their  peripheries  are  bordered  by 
zones  of  the  same  dense  ore.  The  lenses  are  also  traversed  by  quartz 
veins,  the  structure  of  which  is  much  coarser  than  that  of  the  quartz 
mosaic  in  the  fragments.  On  the  other  hand,  their  material  seems  to  be 
identical  with  that  of  the  matrix  in  which  the  fragments  lie.  In  reflected 
light  those  fragments  with  least  of  the  dense  ore  in  them  have  the  bright- 


814  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

red  color  of  jasper,  while  those  in  which  there  is  much  dense  hematite  are 
opaque  and  black.  The  distinction  between  the  jasper  and  the  ore  pebbles 
is  thus  due  solely  to  the  quantity  of  hematite  in  them  and  to  its  character. 

The  groundmass  in  which  these  larger  fragments  are  embedded 
consists  of  smaller  oval  and  lenticular  fragments  of  the  same  kind  as  the 
larger  ones,  cemented  together  by  the  usual  matrix  composed  essentially  of 
interlocking  quartz  grains  materially  larger  than  those  in  the  jasper  frag- 
ments. A  few  of  these  present  the  appearance  of  enlarged  clastic  particles, 
but  by  far  the  greater  portion  were  clearly  formed  in  place.  Tiny  nests 
of  a  ferruginous  carbonate  are  also  noticed  here  and  there.  In  a  few  cases 
zones  of  coarse  quartz  border  the  large  jasper  and  ore  fragments  and 
separate  them  from  the  mosaic  matrix.  Carbonate  nests  also  occur 
frequently  in  the  jasper  pebbles  and  fragments,  where  it  is  clearly 
secondary. 

The  sections  of  many  specimens,  especially  of  the  more  schistose  phases 
of  the  rocks,  are  mottled  with  large  patches  of  quartz,  many  grains  of 
which  are  granulated  on  their  peripheries.  These  patches  are  traversed 
by  broad  veins  of  crystalline  quartz  like  that  composing  the  mosaic 
which  cements  the  granulated  patches  together.  These  rocks  look 
very  much  as  though  they  had  been  crushed  and  shattered  and,  after 
shattering,  had  been  healed  by  deposits  of  silica.  Within  the  patches,  in 
addition  to  the  quartz,  there  are  often  large  quantities  of  a  yellowish, 
probably  ferruginous,  carbonate,  partly  in  granules  and  partly  in  nests, 
and  a  great  number  of  small  particles  of  hematite.  The  cementing  mosaic, 
on  the  other  hand,  is  free  from  carbonate  and  also  practically  free  from 
hematite  dust,  though  an  occasional  speck  of  the  mineral  may  frequently 
be  detected  in  it,  and  here  and  there  a  bunch  of  fibrous  chlorite. 

The  more  distinctly  schistose  these  rocks  the  less  well  preserved  is 
their  fragmental  structure.  The  larger  fragments  in  most  schistose  phases 
are  flattened  almost  into  shreds,  and  the  components  of  the  groundmass 
mosaic  into  distinctly  lenticular  grains.  Wisps  of  muscovite  are  also  devel- 
oped in  the  groundmass,  and  with  them  is  nearly  always  associated  a  little 
calcite  or  othei  colorless  carbonate.  A  few  little  nests  of  the  ferruginous 
carbonate  remain.  Coarse-grained  quartz  veins  cut  through  this  schistose 
groundmass,  and  occasionally  it  is  crossed  by  a  small  vein  of  dense  hema- 
tite.    The  ore  bands  diff'er  from  the  jasper  bands  mainly  in  the  presence  of 


PLATE  XIX. 


315 


PLATE  XIX. 

PHOTOMICROGRAPHS  OF  ROOKS  IN  THE  VULCAN  FORMATION. 

Fig.  a. — Schistose  ferruginous  quartziteat  base  of  Traders  member,  west  end  of  Quinnesec  open  pit. 
Sand  grains  are  inclosed  in  a  matrix  composed  of  smaller  grains  and  narrow  lenses  of  quartz  intermingled 
with  hematite  dust  and  distinct  crystals  of  the  same  mineral.  Some  of  the  hematite  crystals  are  partly 
within  a  quartz  fragment  and  jmrtly  in  the  matrix.  The  schistosity  of  the  hand  specimen  is  due  to 
the  wrapping  of  the  quartz-hematite  matrix  around  the  large  quartz  sand  grains.     Ordinary  light,  X23, 

Fig.  B. — Less  ferruginous  pha.se  of  the  quartzite  at  the  base  of  the  Vulcan  formation.  The  sand 
grains  are  surrounded  by  a  matrix  composed  of  small  grains  and  masses  and  crystals  of  hematite.  The 
fragmental  character  of  the  rock  is  very  plain.  Between  crossed  nicols  all  the  quartz  in  the  matrix 
possesses  the  crystalline  character  of  that  in  typical  jaspers.     Ordinary  light,  Xl5. 

Fig.  C. — Jasper  band  in  jaspilite,  south  side  of  Curry  member,  in  northwest  quarter  of  sec.  13, 
T.  39  N.,  R.  29  W.  The  section  shows  a  finely  crystalline  quartz  aggregate  (which  appears  homoge- 
neous in  ordinary  light)  crossed  by  curved  and  concentric  opaque  bands,  composed  of  little  crystals  of 
hematite.  These  mark  the  outlines  of  what  were  nodules,  which  have  otherwise  entirely  disappeared. 
Ordinary  light,  X23.  Compare  with  photograph  of  ferruginous  chert  derived  from  greenalite. 
Mesabi  district,  Mon.  U.  S.  Geol.  Survey,  vol.  43,  PI.  XV,  A. 

Fig.  D. — Specular  siliceous  ore  from  test  pit  in  the  northwest  quarter  of  sec.  13,  T.  39  N.,  R. 
29  W.,  Curry  member.  The  section  is  made  up  of  elongated  nodules  of  hematite  and  of  jasper  in  a 
homogeneous  mosaic  of  fine-grained  crystallized  quartz.  The  opaque  nodules  are  hematite.  The 
cloudy  ones  are  jasper,  comjiosed  of  hematite  dust  in  a  fine-grained  quartz  mosaic.  One  nodule  shows 
a  concentric  arrangement  of  the  quartz  and  hematite,  characteristic  of  nodules  derived  from  siderite. 
Ordinary  light,  X23. 

Fig.  E. — Spotted  jasper  from  jaspilite,  on  railroad  west  of  the  Verona  mihe.  This  jasper  con- 
sists of  nodules  of  hematite  and  quartz  and  sharp-edged  fragments  of  an  older  jasper  in  a  groundmasa 
of  cherty  quartz.  The  particles  that  are  uniformly  colored  by  hematite  may  be  fragments  of  an  old 
jasper.  Those  with  accumulations  of  hematite  toward  their  centers  are  probably  nodules.  All  particles 
are  surrounded  by  narrow  rims  of  hematite  grains  that  must  have  been  deposited  after  the  rock  had 
practically  assumed  its  present  character.  Ordinary  light,  X23.  Compare  with  photograph  of  ferru- 
ginous chert  derived  from  greenalite.     (iogebic  district,  Mon.  U.  S.  Geol.  Survey,  vol.  43,  PL  XVI,  B. 

Fig.  F. — Same  section.     Under  crossed  nicols  the  entire  field  of  view  breaks  up  into  an  aggregate 
of  finely  crystallized  (cherty)  quartz.     The  outlines  of  a  tew  of  the  nodules  can  be  dimly  discerned, 
but  on  the  whole  the  section  becomes  a  uniform  mosaic,  typical  of  the  jaspers  in  general.     Crossed 
nicols,  X 18.     Compare  PI.  XV,  D,  Mon.  U.  S.  Geol.  Survey,  vol.  43. 
316 


U.   S.   GZOLOGICAL    SURVEY 


MONOGRAPH    XLVl       PL     XIX 


(H) 


(D) 


MICROPHOTOGRAPHS   OF   ROCKS    IN    THE  VULCAN    FORMATION 


ALGONKIAN,  VULCAN  FORMATION.  317 

a  larger  proportion  of  very  much  flattened  ore  fragments  and  partly  in  the 
presence  of  subsequently  deposited  hematite  in  the  form  of  stringers  or 
narrow  veins.  The  proportion  of  the  latter  to  the  former  can  not  be  deter- 
mined, but  in  some  instances  the  newly  deposited  ore  is  present  in  large 
amount. 

The  majority  of  the  mottled  jaspilites  diff'er  from  those  of  Hughitt  Bluff 
in  containing  no  distinctly  characterized  pebbles  of  either  jasper  or  ore. 
Occasionally,  when  the  sections  are  viewed  in  natural  light,  there  can  be 
seen  in  the  siliceous  layers  obscure  traces  of  round  or  oval  quartz  masses 
that  look  something  like  pebbles.  Sometimes  the  center  of  each  mass  is 
occupied  by  a  little  irregular  nucleus  clouded  red  by  minute  particles  of 
hematite.  This  is  surrounded  by  a  zone  of  quartz  in  optical  continuity 
with  the  nucleus  and  meeting  the  peripheries  of  other  grains  in  interlocking 
sutures.  Although  there  seems  to  be  no  sharp  line  of  demarcation  between 
clouded  nucleus  and  clear  periphery,  nevertheless  the  appearance  is  as 
though  the  former  were  sand  grains  that  had  been  enlarged  by  the  addition 
of  new  material.  Again,  in  some  sections  the  distribution  of  hematite 
grains  is  such  as  to  outline  areas  of  quartz  free  from  ore  particles  in  the 
midst  of  an  aggregate  of  quartz  and  ore,  or  the  hematite  is  aggregated  into 
small  spherical  and  lenticular  masses  in  which  the  ore  is  intermingled  with 
a  little  quartz  or  borders  a  little  quartz  area.  In  the  first  case  the  sections 
seem  to  be  composed  of  colorless  pebbles  in  a  crystalline  aggregate  of 
quartz  and  hematite.  In  the  second  case  the  apparent  pebbles  are  probably 
pseudomorjjhs  of  concretions  originally  present  in  the  sediments.  These 
are  much  more  common  in  the  jaspers  of  the  Curry  member,  in  the  discus- 
sion of  which  they  will  be  referred  to  again.  Between  crossed  nicols  the 
fragmental  structure  of  all  sections  disappears,  or,  at  any  rate,  it  becomes 
very  obscure.  The  entire  section  in  each  case  breaks  up  into  a  practically 
uniform  mosaic  of  interlocking  quartz  grains  speckled  with  opaque  dots  and 
ovals  of  hematite  and  occasional  crystals  of  magnetite  (compare  PI.  XIX, 
E  and  F).  In  a  few  of  the  lenticular  areas  outlined  by  the  ore  the  texture 
of  the  mosaic  varies  a  little  from  that  of  the  rest  of  the  section,  but  only  a 
very  little. 

The  ore  layers  of  these  rocks  differ  from  the  siliceous  ones  mainly  in 
the  greater  quantity  of  ore  present.  Most  of  it  is  scattered  in  little  irregu- 
lar masses  between  grains  of  quartz  like  those  in  the  mosaic  composing  the 


318  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

essential  part  of  the  jasper  layers,  but  much  of  it  is  in  long  narrow  string- 
ers that  may  be  flattened  pebbles  or  infiltrations  along  cracks. 

Most  of  the  true  jaspilites  exhibit  no  evidence  of  any  kind  of  having 
ever  contained  fragmeutal  detritus.  Their  jasper  bands  consist  of  a  mosaic 
of  slightly  elongated  quartz  particles  crossed  by  streaks  of  opaque  hematite 
running  in  the  same  direction  as  the  elongation  of  the  quartz  grains.  The 
quartz  grains  are  all  small,  their  dimensions  varying  between  0.07  mm.  and 
0.14  7nm.  along  their  shorter  diameters  and  0.18  mm.  to  0.22  mm.  along  their 
greater  diameters.  The  ore  streaks  are  made  up  of  lines  of  small  crystals 
or  aggregates  of  crystals  that  seem  to  lie  indiff"erently  between  quartz 
grains  and  inclosed  within  them.  Besides  the  ore  inclusions  the  quartz 
contains  also  a  few  liquid  inclusions,  a  few  indeterminate  cloudy  masses, 
some  small  independent  crystals  of  hematite,  and  a  quantity  of  fine  dust- 
like particles  that  may  also  be  a  form  of  iron  oxide.  The  hematite  and 
quartz  look  as  though  they  were  deposited  contemporaneously,  the  rocks  in 
their  microscopical  features  being  identical  with  the  jaspers  of  the  Marquette 
district. 

Occasionally  in  some  sections  small  round  lenticular  areas  of  fine- 
grained quartz  mosaic  are  distinguishable  from  a  surrounding  area  of  coarse 
grain,  and  often  these  are  bounded  by  a  thin  zone  of  ore.  In  other  sec- 
tions there  are  lenticular  and  long,  narrow,  acicular  masses  composed  of 
a  mixture  of  quartz  and  limonite  lying  in  the  usual  quartz  mosaic.  Of 
course  these  phenomena  may  indicate  the  former  presence  of  pebbles  in  the 
original  sediments,  but  the  bodies  are  more  probably  concretions.  They 
are,  however,  by  no  means  as  distinct  as  those  in  the  conglomerates  (see 
p.  303)  or  those  in  the  Curry  jaspers. 

In  some  of  the  layers  the  microscope  shows  that  the  jasper  consists  of 
bands  of  the  usual  quartz  mosaic  interlaminated  with  others  in  which  there 
is  an  abundance  of  a  cloudy,  red  substance,  which  appears  to  be  quartz 
stained  by  a  thin  layer  of  some  iron  hydroxide.  Occasionally  the  red  mat- 
ter is  in  little  plumose  masses  radiating  inward  from  the  peripheries  of  the 
stained  areas,  indicating  plainly  its  secondary  character.  In  other  speci- 
mens round,  cloudy  areas  are  in  reality  portions  of  several  quartz  grains 
filled  with  tiny  liquid  inclusions.  Between  crossed  nicols  these  areas  break 
up  into  aggregates  of  grains  each  of  which  comprises  two  parts,  one  of 
which  is  filled  with   inclusions    and   the  other  entirely  free  from  them. 


ALGONKIAN,  VULCAN  FORMATION.  319 

Neither  of  these  phenomena  can  be  regarded  as  indicating  the  former  pres- 
ence of  pebbles. 

The  most  typical  jaspers — those  which  can  not  be  distinguished 
macroscopically  from  the  typical  jaspers  of  the  Marquette  district,  except 
by  their  more  purple  tinge — differ  from  the  siliceous  bands  above  described 
mainly  in  possessing  a  much  finer  grain.  The  grains  of  their  quartz  mosaic 
rarely  measure  more  than  0.03  mm.  by  0.04  mm.  They  constitute  a  uniform 
aggregate  of  interlocking  particles  thickly  peppered  with  small,  irregular 
flecks  of  ore  and  uniformly  dusted  with  minute  opaque  hematite  grains, 
which  under  high  powers  of  the  microscope  are  resolved  into  little  rods, 
tiny  oval  and  iiTegularly  shaped  bodies,  usually  transparent  in  red  and 
yellow  colors,  and  small,  shai-p-edged  particles  that  resemble  very  small 
fragments.  The  ore  flecks  are  ragged-edged  opaque  masses  with  many 
sharp  projections  that  look  very  much  like  the  corners  of  little  crystals 
extending  beyond  a  compact  aggregate  of  crystals. 

The  distinction  between  jasper  layers  and  ore  layers  in  all  varieties  of 
the  jaspilites  is  due  solely  to  variations  in  the  relative  proportions  of  quartz 
and  hematite  present.  Those  layers  in  which  hematite  is  in  excess  are  the 
ore  layers.  Those  in  which  quartz  predominates  are  jasper  bands.  The 
transition  from  jasper  to  ore  is  usually  accomplished  in  one  of  two  ways. 
In  some  cases  the  dust  particles,  which  have  been  referred  to  as  being 
uniformly  distributed  through  the  quartz  mosaic,  become  aggregated  into 
streaks  and  bands.  Toward  the  borders  of  the  jasper  layers  these  grow 
thicker  and  thicker  and  more  and  more  numerous  until  the  hematite 
exceeds  the  quartz  in  quantity  and  the  layer  loses  its  siliceous  character 
and  passes  into  an  ore  bed.  In  the  second  and  more  frequent  type  of 
transition  the  gradation  is  plainly  the  result  of  a  secondary  deposition. 
Mention  has  been  made  of  the  fact  that  the  quartz  mosaic  of  the  jasper 
bands  is  often  dotted  with  large,  isolated  crystals  of  hematite.  Through 
the  layers,  which  in  the  hand  specimen  are  recognized  as  jasper,  the 
crystals  are  sparsely  scattered  without  any  definite  arrangement  that  can 
be  detected.  As  the  ore  layers  are  approached,  however,  the  crystals 
become  numerous  and  on  the  borders  of  the  bands  they  merge  into  groups 
of  crystals  with  irregular  outlines,  but  usually  with  their  longer  axes 
parallel  to  the  directions  of  the  bands.  In  the  densest  portions  of  the  ore 
layers  these  aggregates  exclude  nearly  all  of  the  quartz,  leaving  just 
enough  remaining  to  enable  one  to  detect  the  presence  of  the  aggregates. 


320  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  ore  layers  in  all  the  jaspilites  thus  differ  from  the  jasper  layers 
merely  in  the  presence  of  a  greater  quantity  of  hematite  of  the  same 
character  as  that  existing  in  the  jasper.  The  structure  of  both  bands  is 
the  same,  althoug'h  the  quartz  in  the  ore  bands  is  usually  freer  from 
hematite  dust  than  that  in  the  jasper  layer.  Although  there  is  usually  a 
gradation  from  jasper  to  ore,  nevertheless  in  some  cases  the  ore  layers  are 
rather  sharply  separated  from  the  jasper  layers  by  a  distinct  line.  Some- 
times there  may  be  a  gradation  on  one  side  of  an  ore  bed  and  a  sharp 
contact  with  the  neighboring  siliceous  bed  on  the  other  side.  Again,  a 
quartz  vein  may  intervene  between  the  two,  in  which  case,  of  course,  their 
separation  is  complete. 

All  the  jaspilites,  whether  of  the  homogeneous  or  of  the  mottled  kind, 
are  without  exception  schistose.  The  elongation  of  the  individual  grains  of 
the  quartz  mosaic,  the  trend  of  the  ore  laminfe,  and  the  position  of  the 
long  axes  of  the  pebble-like  masses  in  the  few  specimens  exhibiting  them, 
are  all  in  the  same  direction,  which  is  also  parallel  to  the  banding.  More- 
over, the  tiny  quartz  veins  that  here  and  there  ramify  the  siliceous  bands 
usually  tend  to  follow  this  same  direction,  and  thus  to  accentuate  the 
schistosity. 

BRIER   SLATE. 
DISTKIBrXION. 

The  Brier  slate  lies  immediately  above  the  Traders  member  and  is 
practically  coextensive  with  it.  Wherever  the  ground  which  is  geologically 
just  above  the  ore-bearing  Traders  member  has  been  explored  the  Brier  slates 
have  been  imcovered.  Where  its  distribution  has  not  been  complicated  by 
faulting  and  profound  folding,  the  slates  occupy  a  continuous  belt  about 
200-400  feet  across,  lying  between  the  Traders  ore  belt  on  one  side  and  the 
Curry  ore  belt  on  the  other.  In  a  few  places  faulting  has  caused  the  slates 
to  disappear  from  the  surface,  and  in  other  places  folding  has  increased 
their  apparent  thickness,  but  in  those  stretches  in  which  the  rocks  have 
not  been  affected  by  disturbances  other  than  those  which  produced  the 
major  folding  of  the  entire  sedimentary  series  the  belt  maintains  a  nearly 
uniform  widtli. 

Along  the  north  side  of  the  Huronian  trough  there  are  no  natural 
exposures  of  the  Brier  slates,  and  explorations  that  have  been  made  in 
the  belt  of  country  immediately  south  of  the  northern  dolomite  belt  have 
nowhere  encountered  the  slates  except  at  the  Loretto   and  the  Appleton 


ALGONKIAN,  VULCAN  FORMATION.  321 

mines,  in  the  extreme  eastern  end  of  the  district.  In  sec.  14,  T.  40  N., 
R.  30  W.,  pits  have  been  opened  up  in  an  iron  formation  which  is  beheved 
to  belong  in  the  Curry  member.  The  Brier  slates  should  be  north  of  these, 
but  drift  hills  cover  the  surface,  and  this  drift  has  not  been  penetrated  by 
exploring  pits  or  shafts.  Therefore  nothing  is  known  of  the  nature  of  the 
rocks  intervening  between  the  ore  pits  near  the  center  of  the  section  and 
the  dolomite  outcrops  near  its  north  quarter  post.  On  the  map  (PI.  IX) 
this  area  is  colored  to  indicate  that  the  underlying  formation  is  not 
known.  The  same  conditions  exist  for  the  entire  belt  between  the  pits 
just  referred  to  and  the  Loretto  mine  in  sec.  7,  T.  39  N.,  R.  28  W.  If  the 
Brier  slate  occurs  along  this  border  of  the  trough  it  is  as  a  narrow  strip  in 
the  area  colored  for  "Formation  not  determinable"  (see  legend  of  map, 
PI.  IX). 

At  the  Loretto  and  Appleton  mines  the  Brier  slate  has  been  encoun- 
tered in  the  underground  workings,  in  diamond-drill  holes,  and  in  numerous 
pits  (see  pp.  404-406)  scattered  over  the  surface  between  the  shafts  of  the 
two  mines.  East  of  the  Appleton  mine  exposures  of  the  Vulcan  formation 
are  unknown.  Its  presence  in  this  area  is  indicated  by  the  existence  of  a 
strong  magnetic  line  (see  p.  286),  but  whether  one  or  all  of  its  members  are 
present  under  the  drift  is  unknown. 

The  distribution  of  the  Vulcan  formation  around  the  central  dolomite 
belt  has  been  described  (pp.  286-287).  At  the  Traders  and  Clifford  pits 
of  the  Traders  mine  the  Brier  slate  is  exjDosed  under  the  stripping  just  above 
the  beds  that  have  yielded  the  merchantable  ore.  It  has  been  discovered 
again  by  drilling  south  of  the  Indiana  mine  between  the  ore-bearing  Traders 
member,  which  has  been  exploited  from  the  Indiana  shaft,  and  a  magnetic 
ore  formation  farther  south.  At  the  Forest  mine,  in  the  southwest  quarter 
of  sec.  25,  T.  40  N.,  R.  30  W.,  several  drill  holes,  located  between  the  main 
iron  formation  in  which  the  mine  shaft  is  sunk  and  a  second  ore  formation 
about  400  feet  south  of  this  shaft,  penetrated  a  dark  slate,  the  position  of 
which  corresponds  to  that  of  the  Brier  slate  elsewhere.  East  of  the  Forest 
mine  for  some  little  distance  the  Algonkian  beds  are  covered  by  the  Lake 
Superior  sandstone,  hence  the  eastward  extension  of  the  Brier  member 
can  be  followed  no  farther.  But  somewhere  between  the  Forest  mine  and 
Iron  Hill,  where  the  Hanbury  slates  are  approximately  in  contact  with  tlie 
Randville  dolomite,  it  disappears  entirely  with  the  rest  of  the  Vulcan  beds. 

.      MON   XLVI^04 21 


322  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  best  exliibition  of  the  Brier  member  is  south  of  the  belt  of  the  Traders 
member  lying  on  the  south  side  of  the  southern  dolomite  belt.  It  is  exposed 
for  nearly  the  entire  lengtli  of  the  district  from  Waucedali  in  the  east  to  the 
Menominee  River  in  the  west.  At  Waucedah  (PI.  XXXVI)  it  has  been 
exposed  for  nearly  a  mile  through  the  north  portion  of  sec.  22,  T.  39  N.,  R. 
28  W.,  by  ledges  and  a  series  of  pits,  the  most  numerous  of  the  latter  lying 
a  short  distance  to  the  northwest  of  the  Emniett  mine.  Between  this  point 
and  the  Sturgeon  River,  a  distance  of  about  2  miles,  no  ledges  of  the  Vulcan 
formation  have  been  found,  nor  has  any  test  pitting  been  done.  A  magnetic 
line  passes  through  sees.  17  and  18,  T.  39  K.,  R.  28  W.,  and  gives  evidence 
of  the  presence  of  the  Vulcan  formation  beneath  the  sands  that  cover  the 
rocks  in  this  portion  of  the  district.  Since,  however,  the  Brier  slate  is  found 
both  at  Waucedah  and  on  the  west  side  of  the  Sturgeon  River  in  sec.  13,  T.  39 
N.,  R.  29  W.,  there  is  no  reason  to  suppose  that  it  is  not  present  in  the  stretch 
of  country  between  these  two  points.  The  evidence  of  its  existence  in  the 
northwest  quarter  of  sec.  13  is  the  presence  of  slates  in  two  pits  about  100 
paces  apart.  North  of  the  northern  slate  pit  are  other  pits  in  an  ore  forma- 
tion which  has  many  of  the  characters  of  the  Traders  member  elsewhere, 
and  south  of  the  southern  pit  is  a  trench  and  a  line  of  pits  exposing  about 
270  feet  of  an  even-bedded  iron  formation  in  the  position  of  tho  Curry 
member.  The  Brier  slate  at  this  place  must  be  between  250  and  300  feet  in 
width.  At  the  Verona  mine,  and  beyond  it  as  far  west  as  the  Aragon  mine, 
the  slate  is  so  well  developed  by  pits,  ledges,  and  the  underground  workings 
of  the  mines  that  there  is  no  question  as  to  its  continuation  throughout  this 
distance  as  a  distinct  and  well- characterized  belt  between  the  Traders  and 
the  Curry  ore  beds.  At  several  points  the  direction  of  the  belt  changes 
to  conform  with  the  folding  of  the  Traders  member.  At  the  Norway  and 
Cyclops  mines  the  slate  is  exposed  at  a  great  number  of  places  in  the  large 
open  pits  of  these  mines  and  in  numerous  small  test  pits.  Its  thickness  is 
increased  by  the  several  folds  that  produced  the  Norway  and  the  Aragon 
basins  and  by  several  minor  folds  superimposed  upon  these  (PI.  XXXI). 
The  presence  of  the  belt  in  sec.  6,  T.  39  N.,  R.  29  W.,  and  in  the  eastern 
half  of  sec.  1,  in  the  next  township  west,  is  doubtful  (see  p.  459).  Near  the 
center  of  sec.  1,  however,  the  entire  Vulcan  series  is  kno.wn  to  disappear  in 
consequence  of  an  overlap.  It  reappears  again  at  Quinnesec  near  the  line 
between  sees.  2  and  3,  in  T.  39  N.,  R.  30  W.     In  the  Quinnesec  fold  the 


ALGONKIAN,  VULCAN  FORMATION.  323 

Brier  slate  is  again  met  with  in  several  belts,  due  to  repetition  of  the  inember 
by  close  folding.  Beyond  Quinnesec  the  Vulcan  formation  is  exposed  by 
drill  holes,  test  pitting,  and  open  mine  pits  as  far  as  the  Pewabic  mine,  but  in 
this  stretch,  so  far  as  known,  it  consists  of  but  two  meinbers — an  iron-bearing 
member  to  the  south  and  a  slate  member  between  this  and  the  dolomite  to 
the  north.  The  iron-bearing  member  is  probably  the  Curry.  The  slate 
member  seems  to  vary  in  thickness,  but  it  never  quite  disappears.  There 
is  always  a  thin  selvage  lying  against  the  dolomite,  and  this  has  the  char- 
acteristics of  the  light-colored  slates  between  the  Traders  member  and  the 
underlying  dolomite.  Where  thicker,  the  upper  portion  of  the  slate 
seems  to  resemble  more  nearly  the  typical  Brier  slate  so  far  as  can  be 
determined  from  the  meager  evidence  at  hand.  These  facts  suggest  that  the 
Brier  slate  in  places,  like  the  Traders  member  throughout  this  portion  of 
the  district,  has  disappeared  and  that  only  where  the  slate  belt  is  thickest 
does  any  of  it  reach  the  present  surface.  The  mapping  is  in  accordance 
with  this  view  (see  map,  PL  XXXVIII).  West  of  the  old  Keel  Ridge 
mine,  in  sec.  32,  T.  40  N.,  R.  30  W.,  is  a  fault,  and  northwest  of  this  fault 
the  entire  Vulcan  formation  again  appears  with  its  three  members.  From 
this  point  to  the  west  end  of  the  Chapin  property  the  Brier  slate  has  been 
exposed  at  many  places,  not  only  in  the  mine  workings,  but  also  by  test  pits 
on  the  surface.  West  of  the  Ludington  mine  the  Vulcan  formation  is 
known  to  occur  as  far  as  the  end  of  the  bluff  in  the  center  of  sec.  26, 
T.  40  N.,  R.  31  W.,  and  many  pits  have  penetrated  it;  but  no  series  of 
openings  exhibits  an  entire  cross  section  of  the  formation;  therefore  it  can 
not  be  stated  definitely  whether  the  Brier  slate  occurs  here  or  not.  On  the 
dump  heaps  of  many  of  the  pits  slates  are  found  which  in  many  respects 
resemble  strongly  some  of  the  weathered  phases  of  the  Brier  member,  but 
not  enough  confidence  is  felt  in  their  identification  to  warrant  their  mapping 
as  such  in  this  portion  of  the  district. 

From  the  fact  that  the  Brier  slate  has  been  recognized  in  all  portions 
of  the  Vulcan  series  where  this  has  been  exposed  from  the  Hanbury  slate 
on  the  one  side  to  the  dolomite  on  the  other,  it  is  believed  that  the  forma- 
tion is  a  constant  one,  and  that  under  normal  conditions  it  will  be  discovered 
everywhere  between  the  Traders  and  Curry  member,  when  exploration  has 
been  sufficiently  thorough  to  open  up  the  ground  between  them. 


324  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

LITHOLOGY. 

Macroscopical. — The  Brier  slates,  in  their  freshest  and  most  typical 
phases,  are  heavy,  black,  dark-gray  or  dark-purple,  very  ferruginous  rocks, 
with  a  dull,  earthy  luster  quite  different  from  the  glistening  luster  of  simi- 
larly colored  slates  belonging  in  the  Hanbury  formation.  The  dull  luster 
is  most  noticeable  on  the  cleavage  surfaces,  which  are  nearly  always  parallel 
to  the  bedding.  On  joint  surfaces  inclined  to  the  bedding  there  can  often 
be  detected  a  little  sheen,  due  to  the  shearing  of  hematite  particles.  Though 
a  few  specimens  exhibit  no  bedding  bands,  the  great  majority  present  a  very 
even  and  fine  banding  in  consequence  of  the  presence  of  layers  richer  than 
the  average  in  iron  oxides  or  of  beds  containing  varying  quantities  of  chlo- 
ritic  or  other  dark  pigments.  This  banding,  which  is  inconspicuous  on  fresh 
surfaces,  is  stronglv  emphasized  by  slight  weathering,  and  consequently, 
since  the  slates  are  very  susceptible  to  weathering  influences,  it  is  a  char- 
acteristic feature  of  most  exposures.  With  slight  weathering  the  bands 
become  gray  and  yellowish-grav,  the  yellowish-gra}'  bands  being  very 
naiTow,  often  not  wider  that  the  thickness  of  a  sheet  of  writing  paper,  and 
the  gra}'  ones  measuring  on  the  average  about  one-fourth  inch  in  width. 
At  the  same  time  the  texture  becomes  sandy,  and  it  is  discovered  that  a 
large  proportion  of  the  rock  consists  of  quartz  grains.  When  the  weather- 
ing is  more  profound,  red  ocher  is  fonned  and  the  slate  becomes  an  alterna- 
tion of  narrow  bands  of  varying  shades  of  yellowish  pink,  red,  and  black. 
Where  the  weathering  has  progressed  very  far,  however,  the  slates  are 
stained  an  almost  uniform  red  color,  in  which  form  they  are  often  indis- 
tinguishable from  certain  phases  of  similarly  stained  Hanbury  slates. 
Usually,  however,  the  Brier  slates  are  much  the  heavier  and  possess  a  darker 
-tinge. 

It  has  already  been  intimated  that  the  Brier  slates  split  easiest  along 
their  bedding  planes.  This  tendency  is  greatly  increased  by  weathering. 
The  rocks  open  between  the  layers,  become  very  shaly,  and  yield 
an  abundant  talus  at  the  bases  of  all  cliffs  in  which  they  are  exposed. 
While  rarely  exhibiting  schistosity,  in  many  places,  especially  where 
folds  have  been  developed,  they  are  crossed  by  joints  inclined  to  the 
bedding,  along  which  they  break  readily,  leaving  fairly  smooth  surfaces. 
Often  the  joints  are  close  together,  and  in  two  systems  intersecting  at  angles 
of  about  70°.  Consequently  the  talus  fragments  are  not  infrequently  small, 
flat  blocks,  diamond  shaped  in  cross  section  and  wedge  shaped  in  vertical 


ALGONKIAN,  VULCAN  FORMATION.  325 

section,  like  the  combinatiou  of  the  prisms  and  basal  planes  in  the  triclinic 
crystal  system. 

Reference  has  also  been  made  to  the  fact  that  the  joint  surfaces  are 
sometimes  made  lustrous  by  shearing.  Movement  along  these  planes  has 
drawn  out  some  of  the  hematite  constituents  and  produced  a  thin  coating 
of  flat  scales,  which  cover  the  surfaces  like  a  thin  layer  of  graphite.  This 
phenomenon  is  not  common,  and  even  when  it  occurs  the  luster  produced 
is  usually  not  more  noticeable  than  would  be  the  case  had  the  dust  from  a 
lead  pencil  been  lightly  rubbed  over  the  surfaces.  In  a  few  instances  the 
coating  is  much  more  marked,  causing  the  rocks  to  look  very  nuich  like 
graphite  slates,  similar  to  some  of  those  in  the  Hanbury  formation.  The 
coating  is  easily  recognized  as  hematite,  however,  by  the  red  color  of  its 
scratched  surface.  Moreover,  the  slate  may  be  distinguished  from  the  Han- 
bury graphite  slates  by  the  fact  that  the  coating  is  not  along  the  main  cleavage 
surfaces,  but  is  on  the  surfaces  of  crevices  that  are  inclined  to  the  cleavage 
at  large  angles.  In  other  instances  the  joint  surfaces  are  covered  by  a 
dense  deposit  of  crystalline  hematite,  which  before  the  rock  is  fractured 
forms  little  veins.  These  usually  run  in  straight  lines  for  long  distances 
corresponding-  to  the  direction  of  the  joints,  but  occasionally  they  fork,  the 
branches  occupying  the  places  of  small  gashes  in  the  rock  or  ending  in 
what  were  little  cavities,  but  which  now  are  minute  bodies  of  ore.  In  a 
few  instances  quartz  was  deposited  in  the  joint  cracks,  and  in  exceptional 
cases  the  joint  surfaces  are  covered  by  druses  of  small  calcite  or  dolomite 
crystals. 

The  typical  slates  above  described  grade  in  several  waj's  into  others 
that  present  quite  diiferent  features.  All  phases,  however,  exhibit  the 
characteristic  fine  unifonu  banding  produced  by  the  alternation  of  thin 
layers  of  different  compositions.  By  iii crease  in  the  quartz  the  slates  may 
become  sandy  in  texture  and  ligliter  in  color.  Alternate  bands  may  be 
gray  and  white,  with  occasional  narrow  lines  of  red  separating  adjacent 
bands,  due  to  the  production  of  ocher  along  the  divisional  planes  between 
the  layers.  On  the  other  hand,  the  earthy  components  may  increase  in 
quantity.  The  slates  thus  become  less  competent  to  resist  strain,  and 
hence  slight  shearing  may  occur  and  the  slate  may  become  schistose.  In 
this  case  the  schistosity  is  nearly  always  parallel  to  the  bedding. 

A  third  distinct  phase  is  produced  by  the  development  of  many  small 
plates  of  glistening  mica.     The  slates  of  this  type  are  usually  of  a  nearly 


326  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

uniform  gray  color,  without  very  distinct  banding.  They  are  more  gran- 
ular than  the  normal  type,  and  because  of  the  luster  of  the  tiny  mica 
plates  they  look  like  fine-grained  quartzites. 

The  most  prevalent  of  the  intermediate  types  are  those  that  connect 
the  normal  slate  with  the  jaspilites  of  the  Curry  member.  The  normal 
Brier  slate  is  a  fairly  dense,  earthy  banded  rock,  containing  a  large 
quantity  of  hematite.  In  the  gradation  phases  there  is  a  more  or  less 
perfect  separation  of  the  iron  oxides  and  the  quartz  and  an  accumulation  of 
these  constituents  in  distinct  bauds,  as  though  they  had  been  more  perfectly 
sorted  by  water  than  in  the  deposition  of  the  normal  rock.  The  layers  in 
which  the  liematite  was  concentrated  thus  became  lean  ore  beds  and  those 
in  which  the  quartz  accumulated  are  impnre  quartzites.  In  the  latter  a 
siliceous  cement  was  deposited,  which  increases  in  quantity  with  nearness 
to  the  Curr}^  beds  and  produces  a  rock  that  more  and  more  closely 
resembles  jasper,  until  finally  the  fragmental  quartz  disappears  entirely  and 
true  jasper  results.  Many  specimens  are  so  completely  intermediate  in 
their  character  that  they  can  not  with  confidence  be  placed  either  in  the 
Brier  or  the  Curry  member,  except  when  their  environment  is  known. 

Microscopical  and  cliemicaL — Under  the  microscope  nearly  all  sections  of 
the  Brier  slates  exhibit  practically  the  same  features.  Small,  sharp-edged, 
fragmental  quartz  grains,  with  a  diameter  of  about  0.1  mm.  and  well-formed 
crystals  of  hematite  with  about  the  same  dimensions,  are  embedded  in  a 
matrix  composed  of  smaller  quartz  fragments  and  crystals  of  hematite 
lying  in  a  still  finer  aggregate  of  quartz  and  a  cloud}-  substance  which 
appears  to  be  a  decomposition  product  of  some  aluminous  mineral,  probably 
feldspar.  The  matrix  contains  a  few  spicules  of  kaolin,  a  little  chlorite, 
and  some  secondary  quartz.  Its  cloudiness  is  due  to  the  presence  of 
innumerable  liematite  particles.  A  comparatively  few  large  flakes  of 
biotite  and  of  muscovite  are  scattered  here  and  there  through  this  matrix 
and  strewn  through  it  in  greater  numbers  are  fragments  of  some  mineral 
stained  red  by  clumps  of  red  ocher.  The  banding  is  caused  by  the  greater 
or  less  abundance  of  the  cloudy  hematitic  matrix  in  the  different  layers. 

The  different  phases  of  the  rock  noticed  in  the  hand  specimens  are 
mainly  due  to  the  varying  proportions  of  the  chlorite  and  magnetite 
present,  and  the  wide  variations  in  the  quantitj'  of  small  quartz  grains  and 
cloudy  material  in  the  matrix.  Where  the  latter  is  in  excess  the  chlorite 
and  kaolin  are  also  abundant.     Their  flakes  are  frequently  arranged  in  a 


ALCxONKIAN,  VULCAN  FORMATION.  327 

parallel  position  which  is  as  often  inclined  to  the  bedding  as  parallel  with 
it.  In  this  way  a  slight  schistosity  is  produced  which  is  inclined  to  the 
bedding,  but  it  is  not  sufficiently  marked  to  be  noticed  macroscopically, 
partly  because  the  quantity  of  the  micaceous  constituents  present  is  always 
small  and  partly  because  of  the  great  abundance  of  crystallized  hematite 
which  serves  as  a  bond  to  hold  tog'ether  the  components  of  the  individual 
layers  and  prevent  easy  fracture  across  them.  Consequently  splitting- 
takes  place  more  easily  between  the  layers  than  across  them  in  the 
direction  of  tlie  schistosity.  When  the  slight  schistosity  is  parallel  to  the 
bedding  the  rocks  naturally  break  especially  easily  in  this  direction. 

Nearly  all  types  of  the  normal  slate  present  the  features  described  above. 
In  a  few  places  the  feldspathic  component  was  originally  so  abunrlant  that 
the  rocks  are  now  practically  clay  slates,  containing  only  here  and  there 
an  isolated  quartz  grain.  These  are  usually  more  schistose  than  the  more 
quartzitie  slates.  The  ferruginous  compounds  are  mainly  earthy  hematite 
or  brown  ocher,  and  this  constituent  is  in  very  flat  lenses  and  in  numerous 
small  oval  bodies. 

In  weathering,  ocher  is  abundantly  produced,  as  has  already  been 
related.  The  chlorite  and  cloudy  material  of  the  matrix  appears  to  yield 
most  freely  to  the  alteration  processes,  and  as  a  result  the  rock  becomes 
a  mass  of  granular  ocherous  material,  in  which  are  embedded  hematite 
crystals  and  quartz  fragments.  Where  the  hematite  crystals  are  surrounded 
by  the  decomposed  matrix  they  are  often  attacked  by  the  weatherino- 
agencies,  with  the  production  of  a  peripheral  zone  of  ocher.  Adjacent 
crystals,  in  contact  with  quartz  only,  remain  unaltered.  Consequently,  it 
frequently  happens  that  the  slates  are  banded  in  dull-red  and  black  bands, 
the  former  representing  layers  in  which  there  was  originally  much  clayey 
or  chloritic  substance  and  the  latter  layers  particularly  rich  in  quartz. 

In  the  last  stages  of  alteration  the  smaller  hematites  and  all  the 
micaceous  and  feldspathic  minerals  have  been  altered  to  limonite,  and  the 
rock  now  consists  of  large  crystals  of  hematite  and  clumps,  grains,  and  rods 
of  brown  ocher  scattered  through  a  colorless  groundmass,  which  under 
crossed  nicols  is  resolved  into  fragments  of  quartz  in  a  matrix  of  crystalline 
quartz;  oi',  if  the  ocher  is  in  great  excess,  the  rock  is  now  composed  of 
fragmental  quartz  grains  in  a  slightly  granular  or  an  almost  homogeneous 
mass  of  ocher. 


328  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

A  second  type  of  the  rock  contains  considerable  carbonate.  kSpecimens 
of  this  type  can  not  be  distinguished  by  the  eye  from  the  sihceous  types. 
Under  the  microscope,  however,  it  is  at  once  noticed  that  the  matrix  often 
consists  of  a  carbonate  in  place  of  quartz  and  feldspathic  material.  The 
crystals  of  hematite  and  the  quartz  fragments  are  less  abundant  than  in 
the  siliceous  tyi^es;  nevertheless  they  are  both  present,  usually  in  consider- 
able quantit}'.  The  hematite  crystals  only  rarely  retain  their  sharp  forms. 
Their  outlines  are  rather  ragged,  and  brown  ocher  or  green  chlorite  nearly 
always  borders  them.  The  appearance  suggests  that  the  crystals  were 
altered  and  that  their  ragged  outlines  are  due  to  corrosion,  which  resulted 
in  the  production  of  the  chloi'ite  and  ocher.  Hematite  grains  and  chlorite 
also  occur  in  aggregates  forming  irregular  masses  embedded  in  the  car- 
bonate. The  latter  mineral  is  a  pale-yellow,  untwinned  variet}^,  which, 
together  with  small  flakes  and  shreds  of  chlorite,  forms  a  matrix  surrounding 
the  hematite  and  quartz  grains.  The  carbonate  is  in  small  grains,  some  of 
which  are  distinct  rhombohedrons,  forming  a  crystalline  aggregate.  It  is 
pi'obable  that  it  is  all  a  secondary  infilti'ation  from  some  outside  source. 
Sometimes  it  occurs  in  rathei"  small  quantities  between  the  fragmental 
grains  of  quartz,  plagioclase,  and  altered  orthoclase  in  a  manner  that  leaves 
no  doubt  as  to  its  secondary  character.  At  other  times  the  fragmental 
grains  are  very  sparse  and  the  chlorite-carbonate  aggregate  makes  up  the 
principal  ^^ortion  of  the  rock,  with  the  ocher  and  hematite  thickly  strewn 
through  it,  often  in  isolated  grains,  masses,  and  crystals,  but  frequently, 
also,  in  narrow  stringers  and  flat  lenses. 

The  banded  character  of  these  .slates,  like  that  of  the  siliceous  kinds, 
is  due  principal!}^  to  the  accumulation  of  the  hematite  in  certain  layers 
and  its  absence  from  others. 

An  analysis  of  the  carbonate,  separated  by  solution  in  nitric  acid 
from  1  gram  of  the  black  slate  occurring  in  the  open  pit  north  of  the 
Curiy  shaft,  gave  Mr.  Allen,  of  the  Survey  laboratory,  the  following  result: 
MgO,  0.0579;  UaO,  0.0810,  and  CO2  in  about  the  proportion  necessary  to 
saturate  the  two  bases.  The  molecular  proportions  of  the  two  bases  are  as 
1  :  1,  and  the  carbonate  is  therefore  a  typical  dolomite,  containing  0.12159 
gram  MgCOg  and  0.14474  gram  CaCOg,  or  a  total  of  0.2663  gram  dolomite 
in  1  gram  of  the  rock.  Thus  26.63  per  cent  of  the  slate  consists  of  the 
dolomite  cement  and  73;37  per  cent  of  insoluble  components. 


ALGONKIAN,  VULCAN  FORMATION.  329 

The  carbonate-bearing  beds  seem  to  be  only  locally  developed.  They 
are  more  noticeable  in  the  neighborhood  of  the  Curry  mine  and  the  No.  3 
shaft  of  the  East  Vulcan  mine  than  elsewhere.  In  the  former  place  the 
overlying  ore  formation  is  cut  by  veins  of  a  ferruginous  carbonate  that  are 
unquestionably  secondary.  At  the  East  Vulcan  locality  there  is  close 
suboinlinate  folding  of  the  slates  and  the  associated  rocks. 

The  gradation  phases  between  the  t3^pical  fragmental  slates  and  the 
jaspilites  of  the  Curry  member  do  not  exhibit  such  features  as  would 
readily  enable  one  to  trace  the  former  into  the  latter.  The  most  frag- 
mental varieties  differ  from  the  typical  Brier  slates  principally  in  being 
finer-grained  and  in  the  possession  of  considerable  crystallized  (i.  e.,  inter- 
locking) quartz  between  the  finer  debris  forming  the  cement  uniting  the 
larger  grains.  Here  and  there  are  large  cloudy  areas  of  light-green  chlorite, 
kaolin,  and  quartz,  probably  representing  decomposed  feldspar  grains,  and 
scattered  all  through  the  section  are  large  and  small  crystals  of  hematite. 
Very  small,  dust-like  jmrticles  of  hematite  are  disseminated  throughout  the 
crystallized  quartz,  and  tiny  irregular  opaque  masses,  that  may  be  this 
mineral  or  magnetite,  occur  in  the  chlorite.  In  some  of  the  sections  there 
is  a  quantity  of  a  micaceous  mineral  in  small  flakes,  filled  with  a  dark- 
brown,  earthy,  ferruginous  compound.  This  is  apparently  a  biotite.  The 
texture  of  these  rocks  is  ver}^  fine  and  in  the  liand  specimen  they  appear 
very  like  a  highly  siliceous  clay  slate.  It  is  probable  that  these  phases 
contained  a  greater  proportion  of  clay  than  most  of  the  rocks  of  the  Brier 
member  and  that  it  is  by  the  decomposition  of  this  substance  that  the 
biotite  originated.  In  these  jjhases,  also,  much  of  the  hematite  is  in  linear 
masses,  which  are  apparently  the  cross  sections  of  platy  aggreg-ates  that 
developed  along  the  bedding  planes.  In  other  cases  large,  irregular  masses 
of  a  semitransparent  red  hematite  occur  here  and  there  through  the  section. 
In  some  places  these  seem  to  have  resulted  from  the  decomposition  of  a  min- 
eral that  has  now  disappeared.  In  other  cases,  however,  the  masses  show  a 
concentric  arrangement  of  layers  around  numerous  centers  like  the  concen- 
tric arrangement  of  opal  in  many  agates.  In  this  form  the  mineral  appears 
to  occupy  little  cavities  in  the  rock.     It  is  unquestionably  an  infiltration. 

In  the  most  jasper-like  phases  of  the  slates  the  grain  is  very  fine.  All 
traces  of  a  fragmental  component  have  disappeared  and  the  rock  is  now 
a  mass  of   interlocking    quartz    surrounding  an  occasional    cloudy  mass, 


330 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


probably  representing  a  decomposed  feldspar,  and  the  usual  crystals  of 
hematite.  In  the  liand  specimen  the  rocks  are  finely  and  evenly  banded 
and  exhibit  close  relationship  with  the  slates.  .  In  thin  section  the  speci- 
mens resemble  very  closely  some  of  the  jaspilites  except  that  the  iron 
oxides  are  not  so  dense  and  the  quartz  is  less  clear.  Its  cloudiness  is  due 
mainly  to  the  presence  of  little  flakes  of  kaolin,  shreds  of  muscovite,  parti- 
cles of  hematite,  and  a  host  of  tiny  dust  g-rains  of  various  kinds,  too  small 
to  be  satisfactorily  identified. 

Two  analyses  of  Brier  slates  follow.  The  first  is  of  a  specimen  from 
the  cut  along  the  railroad  north  of  Curry  shaft  No.  1,  sec.  9,  T.  39  N., 
R.  29  W.  It  was  made  by  Mr.  E.  T.  Allen  in  the  Survey  laboratory.  The 
second  is  an  analysis  of  the  foot  slates  on  the  fifth  level  of  the  Chapin 
mine.     This  was  furnished  by  Mr.  E.  E.  Brewster. 

Analyses  of  Brier  slates. 


i. 

II. 

SiO,^                                       

50. 15 

.  8S03 ' 
6.55 

.0642 
38.80 

.2112 
94 

.0131 

.94 

.0233 

.16 

.31 

.  0050 
4.38 

.0466 

.81 

.0450 
1.43 

.0794 

.52 

.08 

Tr. 

Tr. 

54.13 

ALO, 

.8962 
13.53 

re.,0..                                

.1326 

PeO 

21.23 

M^O 

4.24 

CaO                                

.1052 

Na^O 

.03 

K,0                     1. 

3.29 

H./J  at  105° 

.0350 

H.,0  above  105° 

«  2.  95 
.1639 

TiO, 

PA 

S 

Cr^Oa 

100.  07 

99.40 

3  on  Ignition. 


ALGONKIAN,  VULCAN  FORMATION.  331 

From  these  two  analyses  it  is  seen  that  the  Brier  slates  differ  materially 
from  the  Traders  slates  in  the  higher  percentage  of  silica  present  and 
greater  abundance  of  ferrous  iron.  The  former  must  be  ascribed  to  quartz 
and  the  latter  to  hematite.  The  potash  and  most  of  the  alumina  are 
probably  in  orthoclase  or  its  decomposition  products,  kaolin  and  muscovite. 
These  constituents,  together  with  the  silica  present  in'  tlie  remaining  ones, 
make  up  about  94  jjer  cent  of  the  slate,  the  composition  of  which  is  given 
under  I,  leaving  onlj^  6  per  cent  to  be  distributed  among  the  biotite,  chlorite, 
and  other  minerals  present.  Of  the  silica  present  about  30  per  cent  must 
be  in  the  form  of  quartz. 

CURKY    MEMBER. 
DISTRIBUTION. 

The  iron-bearing  Curry  member  lies  immediately  above  the  Brier 
slate,  completing  the  series  of  beds  compreiiended  in  the  Vulcan  formation. 
It  is  probable  that  it  is  more  widely  spread  over  the  district  than  either 
the  Traders  member  or  the  Brier  slate,  though  it  can  not  everywhere  be 
definitely  identified.  Wherever  the  Brier  slate  has  been  recognized,  except 
where  it  occurs  as  small  remnants  preserved  ^from  erosion  on  the  top  of 
Traders  beds,  the  Curry  member  has  been  discovered  closely  associated 
with  it  and  always  between  it  and  the  Hanbury  slates.  Moreover,  in 
several  belts  of  country  from  which  the  Brier  slates  are  absent,  but  in 
which  some  of  the  Vulcan  formation  is  present,  this  member  is  believed  to 
be  the  Curry  member.  However,  the  continuity  of  the  Curry  beds  is  not 
so  well  established  as  that  of  the  lower  members  of  the  formation  for  the 
reason  that  it  has  not  been  as  thoroughly  explored.  Fewer  valuable  ore 
deposits  have  been  discovered  in  it  than  in  the  Traders  member,  and 
consequently  it  has  not  been  thought  worth  while  to  explore  it  as  carefully. 

On  the  north  side  of  the  Huronian  trough  the  only  places  at  which 
the  Vulcan  formation  is  known  to  occur  are  in  sec.  14,  T.  40  N.,  R.  30  W., 
and  at  the  Loretto  and  Appleton  mines,  in  sec.  7,  T.  39  N.,  R.  28  W.  In 
the  first-mentioned  locality  the  rock  is  exposed  only  in  pits,  but  since  the 
character  of  the  material  on  the  dumps  is  more  like  that  of  the  Curry 
member  than  like  that  of  the  Traders  member  where  this  has  been  seen 
elsewhere,  the  underlying  iron-bearing  series  is  thought  to  be  the  Curry. 
At  the  Loretto  and  the  Appleton  mines  there  are  few  outcrops  now  visible, 
and  none  of  these  are  of  rocks  belonging  with  the  Curry  beds.     Pits  and 


332  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

drill  holes  have  exposed  siliceous  slates  like  those  belonging  in  the  Brier 
member,  underlain  by  an  iron-bearing  series  closely  resembling  the  beds 
of  the  Traders  member.  The  slates  are  the  youngest  Huronian  rocks  yet 
disclosed  in  this  vicinity.  They  are  now  at  the  surface;  the  Curry  member, 
which  overlies  these  stratigraphically,  has  been  removed  by  erosion. 

Since  the  Loretto  beds  are  in  an  eastern-pitching  syncline  and  a 
southern-dipping  monocline,  the  Curry  member  may  still  exist  to  the  east 
of  the  Appleton  mine  and  to  the  south  of  this  and  the  Loretto  mine,  but 
if  so,  there  is,  as  yet,  no  evidence  to  this  effect,  as  the  country  to  the  east 
and  south  of  these  mines  has  not  been  explored  and  there  are  no  natural 
outcrops  of  the  Vulcan  formation  in  either  area.  Near  the  mine  the  surface 
is  covered  with  sand,  and,  farther  away,  by  a  thick  layer  of  sandstone. 

In  the  center  of  the  trovigh  the  Curi-y  member  exists  at  the  Traders 
and  the  Old  Indiana  mines,  but  it  has  not  been  encountered  elsewhere.  At 
the  Traders  mine  (PI.  XXIV)  there  are  two  pits  in  an  iron  formation  north 
of  the  compressor  at  the  end  of  the  trestle  extending  from  the  Traders 
mine  pit,  and  between  these  and  the  main  ore  deposit  of  the  mine  is  a  belt 
over  200  feet  wide  in  which  are  pits  of  Brier  slate.  Moreover,  at  320  feet 
west  of  the  compressor,  on  the  north  side  of  the  railroad  running  into  the 
Clifford  pit  of  the  same  mine,  is  a  small  exploration  that  uncovered  graphitic 
slates  belonging  at  or  near  the  bottom  of  the  Haubury  formation.  In  this 
interval  there  is  scarcely  room  for  the  full  development  of  the  Curry 
member,  but  since  the  graphite-slates  must  be  very  near  the  eastern  limit 
of  the  Hanbury  formation  at  this  place,  it  seems  necessary  to  assume  that 
the  Curry  beds  occupy  the  space. 

The  presence  of  the  Curry  member  at  the  Old  Indiana  mine  is  shown 
by  drill  holes  south  of  the  slate  member  south  of  the  Indiana  ore  beds. 
At  this  place  the  Curry  beds  are  magnetic. 

At  the  Forest  mine  exploration  has  not  proceeded  far  enough  at  this 
writing  to  warrant  a  statement  as  to  the  absence  or  presence  of  the  Curry 
member,  but  since  a  belt  of  slates  350  to  400  feet  wide  is  known  to  exist 
between  two  belts  of  ore-bearing  beds  it  is  probable  that  the  southern  of 
these  is  of  Curry  age. 

The  best  development  of  the  Curry  member  is  in  the  belt  lying  south 
of  the  southern  dolomite  belt.  At  Waucedah  it  is  exposed  in  the  Emmett 
and  Breen  pits  (PI.  XXXVl),  and  it  has  been  traced  by  test  pits  and  ledges 


ALGONKIAN,  VULCAN  FORMATION.  333 

westward  for  a  distance  of  about  three-fourths  of  a  mile.  It  has  again  been 
uncovered  by  a  trench  and  test  pits  in  sec.  13.  T.  39  N.,  R.  29  W.,  and  has 
been  opened  up  by  exploring-  pits  and  mine  workings  as  far  west  as  the 
Aragon  mine.  For  a  short  distance  beyond  this  point  only  one  ore-bearing 
series  has  been  found.  It  was  traced  to  the  west  side  of  sec.  6,  T.  39  N., 
R.  29  W.,  where  it  gradually  disappears  by  the  overlap  of  the  Hanbury  slate, 
which  has  buried  the  entire  Vulcan  formation  in  sec.  1,  T.  39  N.,  R.  30  W. 
On  the  Cundy,  the  Pewabic,  and  the  Ohapin  properties  there  is  abundant 
evidence  of  the  presence  of  the  Curry  member,  not  only  in  the  underground 
workings  of  the  respective  mines,  but  also  in  the  surface  pittings  and  occa- 
sionally in  ledges.  Between  the  Cundy  and  the  Pewabic  mines  and 
between  the  Ludington  mine  and  the  Menominee  River  only  one  iron- 
bearing  horizon  has  been  detected.  It  is  true  that  in  these  two  stretches 
the  explorations  are  mainl}-  limited  to  the  lower  portion  of  the  Vulcan  for- 
mation, but  here  and  there  test  pits  and  drill  holes  show  that  the  ore-bear- 
ing horizon  is  narrow,  and  that  there  is  not  sufficient  room  between  the 
known  position  of  iron-bearing  series  that  has  been  located  and  the  slates 
regarded  as  Hanbury  slates  to  the  south  to  admit  of  the  occurrence  between 
them  of  the  Brier  slates  and  the  Curry  beds.  The  iron-bearing  series  in 
these  two  portions  of  the  Vulcan  belt  is  therefore  placed  provisionally  in  the 
Curry  member,  the  underlying  Brier  slates  and  the  Traders  beds  being 
considered  as  having  disappeared  by  overlap.  If  the  southern  slates  are  not 
members  of  the  Hanbur}^  formation,  but  are  Brier,  then  the  iron-bearing 
series  would  have  the  position  of  the  Traders  bed  (see  pp.  456-457). 

LITHOLOGT. 

Macroscopical — The  rocks  of  the  Curry  member  comprise  even-bedded 
jaspilites  and  quartzose  slates  and  irregulai'-shaped  ore  deposits  intersecting 
the  bedded  series  more  commonly  at  or  near  their  base  than  elsewhere. 
There  are  present  also  locally  developed  interbedded  cherts  and  hematite 
layers.  These  are  much  more  common  than  they  are  in  the  Traders  mem- 
ber, nevertheless  they  are  greatly  subordinate  to  the  jaspilites,  from  which 
they  seem  to  differ  principally  in  the  color  of  the  siliceous  component.  Of 
the  jaspilites  two  distinct  vai'ieties  are  recognizable.  The  first  resembles 
strongly  the  corresponding  rocks  in  the  Traders  member.  These  are  even- 
banded,  dark-purple,  sometimes  almost  black  varieties,  consisting  of  inter- 
laminated  layers  of  jasper  and  ore.     The  former  are  in  beds  that  vary  in 


334  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

thickness  from  a  small  fraction  of  an  inch  to  nearly  2  inches.  The  jasper 
is  dark  purple  in  color,  a  little  denser  and  more  flinty  than  the  greater  por- 
tion of  the  jasper  in  the  Traders  member,  and  very  much  like  the  dense 
variety  near  the  base  of  the  member.  Occasionally  this  jasper  has  the 
gi-anular  appearance  characteristic  of  the  major  portion  of  the  Traders 
jasper  and  rarelv  it  exhibits  the  spotted  appearance  so  noticeable  in  this 
rock — a  structure  which,  in  the  Traders  jaspers,  was  regarded  as  indicating 
the  presence  of  fragments  of  jasper  derived  from  some  preexisting  source. 
The  ore  bands  are  usually  much  thinner  than  the  jasper  layers,  thoug-h 
occasionally  they  reach  a  considerable  thickness  through  the  replacement 
of  the  jasper  by  hematite.  More  commonly  the  individual  ore  bands  are 
not  more  than  one-tenth  inch  thick,  the  apparently  thicker  bands  being 
made  up  of  a  great  number  of  laminji?  of  the  thickness  of  a  sheet  of  writing 
j^aper.  Between  them  are  equally  thin  layers  of  jasper.  Because  of  their 
composite  character  nearly  all  the  hematite  layers  of  this  variety  have  a 
stratified  appearance.  In  all  cases  the  stratification  is  parallel  to  the 
banding  produced  by  the  alternation  of  ore  and  jasjjer.  The  material  of 
the  ore  bands  is  a  hard,  dense,  flinty,  steel-gray  hematite  without  definite 
structiu'e.  It  resembles  closely  the  dense  black  ore  forming  the  small  veins 
in  the  Traders  beds. 

None  of  the  jaspilites  of  this  type  present  any  evidence  of  the  intense 
shearing  to  which  the  Traders  jaspilites  have  been  subjected.  This  may 
be  due  to  the  fact  that  the  Curry  beds  are  at  a  greater  distance  from  the 
contact  plane  between  the  Lower  and  the  Upper  Menominee  series. 

The  second  and  more  common  form  of  the  Curry  jaspilites  diff'ers  con- 
siderablv  from  the  form  just  described  and  has  practically  no  counterpart  in 
the  Traders  member.  This  type,  although  distinctly  banded,  has  not  usually 
the  definite  clear-cut  banding  characterizing  the  first  type,  nor  is  the  con- 
tact between  siliceous  and  ferruginous  bands  as  striking.  The  materials 
are  more  or  less  thoroughly  intermingled,  the  jasper  bands  containing  a 
large  proportion  of  hematite  and  the  ore  bands  containing  much  silica. 
Where  the  two  kinds  of  material  are  most  distincth'  differentiated  the 
siliceous  bands  can  be  made  out  to  be  long,  flat  lenses,  overlapped  at  the 
ends  by  the  ferruginous  material.  Toward  their  edges  and  ends  the  jasper 
passes  over  gradually  into  ore.  The  jasperized  bands  are  sometimes  dark 
red  or  purple,  but  more  frequently  they  are  dark  pinkish-gray  and  cherty 


ALGONKIAN,  VULCAN  FORMATION.  335 

looking.  In  some  places  the  siliceous  bands  are  well-characterized  chert 
of  a  light  gray  or  nearly  white  color,  but,  as  before  stated,  these  varieties 
are  only  locally  developed.  In  other  places  narrow  seams  of  the  white 
chert  penetrate  the  jasper  and  the  ore  bands  along  their  bedding  planes, 
and  sometimes  they  occur  between  the  ore  and  the  jasper.  In  the  latter 
case  the  chert  seems  to  be  a  vein  filling;  in  the  former  cases  it  is  similar 
to  the  normal  jasper  in  all  respects  save  color. 

In  every  instance  the  siliceous  material  is  granular  looking,  as  though 
it  were  composed  largely  of  sand  grains.  In  some  specimens  this  texture  is 
so  marked  tliafthe  rock  resembles  closely  a  fine-grained  quartzite  or  a  dense 
sandstone. 

The  ore  associated  with  the  jasper  is  also  sand}'  looking,  as  though 
it  were  mixed  with  an  appreciable  quantity  of  sand  grains  or  were  itself 
a  mass  of  small  fragments.  Upon  close  inspection  it  is  found  to  consist  of 
many  little  plates  of  hematite  lying-  in  one  direction,  which  is  the  same 
as  that  of  the  banding  of  the  jaspilites,  and  innumerable  little  crystals  of 
the  same  mineral,  with  glistening  surfaces.  On  cleavage  surfaces  the  ore 
sometimes  presents  a.  micaceous  appearance,  but  the  plates  are  small  and 
the  sti'ucture  is  therefore  by  no  means  as  marked  as  in  the  micaceous  ores 
of  the  Traders  member.  More  frequently  the  surface  is  slightly  rough  and 
granular,  like  that  of  a  poorly  cleavable  clay  slate.  The  splitting  appears 
to  have  taken  place  between  two  sedimentary  layers  which  had  not  been 
moved  with  respect  to  one  another.  In  some  specimens  the  arrangement 
of  the  little  ore  particles  is  so  regular  that  the  rock  appears  to  be  schistose 
throughout,  and  this  structural  feature  is  often  emphasized  by  the 
occuri-ence  within  the  ore  of  many  small  lenses  of  jasper  with  tlieir  long 
axes  in  the  plane  of  the  apparent  schistosity.  Usually,  however,  the  ore 
presents  no  appearance  of  schistosity  but  is  a  dense,  fine-grained,  lusterless 
aggregate  of  small  grains  of  hematite  with  occasional  fiakes  of  a  light- 
colored  micaceous  mineral,  which  the  study  of  thin  sections  shows  to  be 
muscovite.  Like  the  ore  bands  of  the  first  kind,  those  of  the  sandy  texture 
are  also  very  frequently  laminated,  tlie  laminae  sometimes  consisting  of 
alternating  thin  layers  of  jasper  and  ore  and  sometimes  of  light-  and  dark- 
colored  ore. 

Mention  has  been  made  of  the  fact  that  the  banding  of  the  sandy 
jaspilites  is  not  as  distinct  as  that  of  the  denser  variety,  because  of  the 


336  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

gradation  of  the  siliceous  into  the  fer  uginous  layers.  In  some  few  cases, 
however,  the  banding  is  quite  definite,  especially  where  the  siliceous  layer 
consists  of  gray  chert  in  place  of  purple  jasper;  but  this  definiteness  is 
usually  more  apparent  than  real.  The  borders  of  the  chert  layers  are 
often  stained  by  dark-red  iron  oxides  or  they  are  bleached  to  a  white  color. 
Where  the  alteration  has  ])roceeded  inward  to  a  uniform  distance  a  sharp 
line  of  demarcation  occurs  between  the  altered  and  the  unaltered  chert, 
and  thus  a  definite  band  of  gray  chert  between  white  borders  is  produced, 
or  a  gray  band  with  a  uniform  thickness  for  some  distance  is  bordered  by 
narrow  dark-red,  bands  that  grade  off  gradually  into  the  black  ore.  In 
either  case  the  siliceous  bands  seem  to  be  regular  and  continuous,  but 
when  closeh'  inspected  in  large  hand  specimens  and  in  the  ledge  they  may 
be  seen  to  wedge  out  at  each  end,  i.  e.,  to  be  large  flat  lenses. 

The  flinty  and  the  sandy  jaspilites  grade  into  one  another  both  through 
the  ore  bands  and  the  jasper  layers,  but  more  commonly  through  the  latter. 
The  gradation  phases  of  the  ore  are  identical  in  appearance  with  the  mottled 
ores  of  the  Traders  member.  On  fresh  cleavage  surfaces  little  dots  of 
glistening  micaceous  oi'e  are  interspersed  through  a  less  brilliantly  reflecting 
mass  of  the  same  mineral.  In  the  jasper  layers  a  distinct  mottling  is  also 
apparent.  Little  oval  particles  of  a  bright-red  or  dull-purple  jasper  are 
thickly  strewn  through  a  dark-purple  or  purplish-gray  matrix,  in  which  lie 
also  minute  lenses  of  ore  measuring  one-half  millimeter  or  less  along  their 
larger  axes.  With  the  increase  in  the  number  of  inclosed  particles  of  jasper 
in  the  siliceous  bands  and  of  ore  particles  in  the  hematite  bands  these 
assume  more  and  more  the  characters  of  the  flinty  jasper  and  the  micaceous 
ores  until  finally,  with  the  entire  disappearance  of  the  matrices,  the  rocks 
pass  over  into  the  typical  flinty  jaspilites. 

Although  rarely  schistose  to  any  great  extent  the  Curry  jaspilites  are 
jointed  and  gashed  in  a  few  places.  Hematite  has  sometimes  entered  the 
cracks  thus  formed  and  veinlets  of  ore  have  resulted.  When  parted  along 
these  joint  cracks  their  surfaces  are  found  to  be  coated  by  druses  of  tiny 
hematite  crystals.  At  the  angles  between  intersecting  joints  the  jasper  is 
sometimes  crushed  to  a  fine  breccia  and  the  fragments  thus  produced  are 
cemented  together  by  quartz  or  hematite.  In  other  instances  the  cracks 
and  open  spaces  in  the  rock  are  filled  with  a  yellow  clay -like  ocher,  or  with 
druses  of  yellowish-brown  calcite  crystals.      Small  veins    of  quartz   and  of 


ALGONKIAN,  VULCAN  FORMATION.  337 

calcite  also  traverse  the  rock  in  divers  directions,  and  narrow  seams  of  white 
chert  are  interposed  between  the  ore  and  jasper  bands,  or  penetrate  the  ore 
and  the  jasper  bands  parallel  to  their  bedding.  In  either  case  they  seem  to 
have  insinuated  themselves  between  the  laminae,  which  separate  readily  in 
many  instances,  especially  in  the  ores,  and  give  these  a  platy  structure. 
In  other  cases  larger  open  veins  of  crystallized  calcite  occur  cutting  through 
the  ore  bands  approximately,  but  not  quite  parallel  to  their  lamination. 
The  laminse.  are  cut  across  obliquely,  showing  that  the  openings  were  made, 
not  b}'  separation  of  lamina?,  but  by  solution.  The  ore  bordering  the  veins 
is  saturated  with  calcite  for  a  distance  of  about  one-half  an  inch  from  the 
liorders  of  the  veins  and  the  walls  of  the  openings  are  lined  with  druses  of 
small  white  or  brown-stained  crystals  that  are  modified  rhombohedrons. 
Here  and  there  the  vein  widens  and  large  vugs  partially  filled  with  crystals 
are  developed.  These  veins  are  quite  distinct  from  the  veins  of  granular 
red  carbonate  cutting  the  rocks  in  the  neighborhood  of  the  Currj^  mine 
(see  p.  339).  These  phenomena  indicate  that  the  Curry  member  has 
suffered  considerable  fracture  since  its  deposition.  Its  deformation  bv 
this  process  was,  however,  by  no  means  so  severe  as  that  of  the  underlying- 
Traders  member.  It  will  be  observed  later  that  its  folding  was  likewise  less 
severe.  The  reason  for  this  is  probably  that  the  Ciu-ry  member  lies  above 
a  slate  belt  which  absorbed  most  of  the  stresses  to  which  the  formation 
was  subjected  while  the  Traders  member  lay  between  these  slates  and  an 
imderlying  very  competent  dolomite  bed  that  transmitted  the  stresses 
almost  unimpaired. 

The  interbedded  quartz-slates  and  ores  differ  markedly  from  the 
jaspilites  described  in  the  foregoing  paragraphs  in  the  fact  that  they  are 
not  definitely  banded  in  distinct  jasper  and  ore  bands,  but,  on  the  contrarj-, 
are  made  up  of  a  regularly  interlaminated  series  of  thin  ferruginous  and 
siliceous  layers  forming  a  rock  with  nearly  uniform  characteristics  through- 
out. In  many  instances,  it  is  true,  the  siliceous  layers  predominate  through 
a  thickness  of  one-fourth  to  1  inch,  and  these  are  followed  by  a  thickness 
of  the  same  extent  in  which  the  ferruginous  laminse  predominate.  Thus 
a  certain  sort  of  a  banding  is  produced,  but  the  contrast  between  the 
contiguous  bands  is  very  slight,  since  each  is  composite,  being  made  up  of 
laminae  of  the  same  materials  but  in  slightly  diff'erent  jJi'oportions.  As  may 
be  inferred  from  what  has  been  stated,  these  rocks   are  all    beautifull}- 

MON  XLVI — 04 22 


338  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

laminated,  and  because  cleavage  takes  place  so  readily  between  the  laminae 
they  are  often  jilaty  in  structure.  In  many  places  the  layers  are  so  ricJi  in 
iron  oxides  that  they  almost  constitute  lean  ores.  Where  enriched  by  a 
secondary  deposition  of  hematite,  as  at  the  Curry  mine,  they  furnish  an  ore 
of  considerable  value. 

In  their  general  aspects  the  quartzose  slates  and  interbedded  ores  look 
very  much  like  the  more  ferruginous  forms  of  the  Brier  slate.  They  are 
found  most  frequently  at  or  near  the  base  of  the  Curry  member,  passing 
below  into  the  slates  by  gradual  transitions  through  the  increase  in  number 
and  size  of  the  siliceous  layers  and  upward  into  the  banded  jaspilites  by 
the  aggregation  of  the  ore  laminte  into  layers  and  the  gradual  passage  of 
the  siliceous  layers  into  jasper  layers,  partly  through  the  withdrawal  of  the 
more  highly  ferruginous  laminje  and  the  further  silicification  of  the  remain- 
ing material  by  the  deposition  of  secondary  quartz.  The  resemblance  of 
some  of  the  rocks  to  the  Brier  slates  is  so  striking  that  it  seems  necessary 
to  infer  that  they  were  formed  by  the  gradual  replacement  of  the  slates  by 
ferruginous  material.  All  these  rocks  are  dark  brown  or  black  and  very 
fine  grained.  Some  of  the  layers  occasionally  have  a  greenish  tinge  because 
of  the  presence  of  chlorite,  but  this  is  rare.  Occasionally  there  are  also 
met  with  a  few  layers  of  a  pinkish-gray,  fine-grained  quartzite  and  some- 
times a  layer  or  vein  of  gray  chert  interlaminated  with  the  more  usual  type. 

None  of  the  beds  are  schistose,  but  in  some  of  them  the  ore  and  other 
particles  are  platy,  with  their  long  directions  lying  in  the  plane  of  the  bed- 
ding, and  in  these  cases  the  cleavage  surfaces  parallel  to  the  bedding  are 
somewhat  lustrous. 

At  the  Klondike  shaft  of  the  AA^est  A^ulcan  mine,  in  the  northwest 
quarter  of  the  southwest  quarter  of  sec.  10,  T.  39  N.,  R.  29  AV.,  there  is 
intimately  associated  with  the  ore  in  the  dump  a  light-gray  calcareous 
cherty  rock  quite  different  from  the  usual  cherts  of  the  formation.  This 
occurs  in  bands  or  layers  one-half  inch  or  less  thick,  interlaminated  with 
a  dense  black  ore.  The  ore  appears  to  grade  into  the  chert  and  to  cut 
it  in  numerous  tiny  veins.  Although  dense  as  a  rule,  the  chert  contains 
some  open  cavities,  and  on  the  walls  of  these  are  druses  of  crystallized 
hematite.  A  rock  resembling  this  in  its  external  aspects  has  also  been 
found  on  the  south  side  of  the  Curry  ore  beds  on  the  fifteenth  level  of  the 
Vulcan  mine,  about  1,200  feet  below  the  collar  of  the  shaft.  Here  it  is 
distinctly  laminated  parallel  to   the   bedding,   and  is  crossed  by  at  least 


ALGONKIAN,  VULCAN  FORMATION.  339 

four  systems  of  joint  cracks,  most  of  which  are  filled  with  a  dark-green 
earthy  chlorite.  On  the  thirteenth  level  of  the  same  mine,  about  400  feet 
east  of  the  locality  on  the  fifteenth  level  and  about  1 40  feet  above  it,  the 
same  rock  seems  to  have  been  met  with  again.  At  this  place  it  is  more 
massive  and  less  distinctly  stratified,  and  is  extremely  I'ich  in  pyrite,  which 
is  uniformly  distributed  through  it  in  small  grains  and  irregular  masses 
rather  than  in  veins.  These  rocks  will  be  referred  to  again  in  the  descriptions 
of  the  West  Vulcan  ore  deposits  (p.  439). 

In  the  neighborhood  of  the  Curry  mine  the  rocks  of  the  Cuny  luember 
are  traversed  by  coarse-grained  veins  of  a  dark-pink  dolomite.  Some  of 
the  narrower  veins  and  a  few  of  the  coarser  ones  cross  the  beds  diagonally, 
but  most  of  them  run  parallel  to  the  bedding  and  preferablv  along  the 
contact  between  neighboring  beds.  The  same  carbonate  occurs  also 
disseminated  as  small  crystals  through  the  ore,  and  in  some  beds  it  forms 
a  matrix  in  which  ore  particles  and  small  masses  are  scattered.  In  this 
form  the  ore  looks  like  a  granular  ag'gregate  of  hematite  and  carbonate. 
In  other  places  certain  of  the  ore  bands,  which  upon  casual  inspection  look 
no  different  from  the  contiguous  ones,  are  found  upon  closer  study  to  be 
saturated  with  carbonate.  This  reveals  itself  only  in  broken  cross  sections 
when  the  bands  fracture  along  the  cleavage  planes  of  the  carbonate  and 
consequently  reflect  uniformly  from  large  surfaces.  Often  a  narrow  layer 
will  reflect  evenly  for  distances  of  2  inches  or  more,  while  the  neighboring- 
bands  are  completely  devoid  of  such  reflecting  surfaces.  The  rocks  seem 
to  be  well  impregnated  with  carbonate,  but  this  appears  to  have  selected 
for  saturation  certain  definite  layers.  These  carbonated  ox'es  are  gray  when 
fresh  and  brown  where  weathered. 

Microscopical. — The  flinty,  or  more  typically  cherty,  jaspilites  of  the 
Curry  member  differ  very  little  from  the  corresponding  rocks  of  the 
Traders  member.  In  the  siliceous  layers  quartz  predominates,  though  ore 
particles  are  often  present  in  great  numbers.  The  majority  of  these  consist 
of  hematite  in  small  opaque  crystals  and  in  minute  transparent  plates. 
Another  portion,  and  a  much  larger  portion  than  in  the  Traders  jaspers, 
consists  of  large  crystals  of  hematite  and  of  magnetite.  These  ore  particles 
are  often  disseminated  through  the  quartz  grains,  but  more  frequently  they 
lie  between  them.  For  the  most  jjart  they  are  distributed  uniformly,  but 
in  nearly  all  sections  it  is  observed  that  the  hematite  especially,  and 
sometimes  the  magnetite,  is  arranged  along  lines  that  run  in  the  direction 


340  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

of  the  rock  bedding.  Besides  these  two  iron  oxides  there  is  also  present 
in  a  laroe   number  of  sections   an  abundance  of  brown  ocher  which  is 

CD 

usually  in  small  irregular  masses  between  the  quartz  grains.  The  latter 
hiterlock  in  the  usual  manner  characteristic  of  the  jaspers.  Liquid 
inclusions  containing  bubbles,  some  of  which  are  movable,  are  common 
in  them  and  strain  shadows  are  almost  universal,  more  particularly  in 
those  specimens  in  which  the  grains  are  elongated.  Besides  the  minerals 
mentioned,  the  jaspers  of  this  kind  often  contain  also  small  plates  and 
wisps  of  a  light-green  chlorite,  an  occasional  shred  of  kaolin  or  sericite, 
and  little  grains  of  a  highl}'  refractive,  light-j-ellow,  transparent  substance 
that  yields  ocher  by  decomposition.  This  was  at  iirst  thought  to  be 
siderite,  but  since  it  is  not  attacked  by  hydrochloric  acid  it  can  not  be  a 
carbonate.  An  undoubted  carbonate,  which  from  its  color  is  supposed  to 
contain  some  iron,  is  present  in  little  nests  here  and  there  through  the  rock. 
This  is  plainly  secondary. 

The  banding  of  these  jaspilites,  like  that  of  the  Traders  jas^jilites,  is 
due  to  layers  alternately  richer  and  poorer  in  hematite,  in  structure  and 
composition  the  ferruginous  bands  are  not  esseutiall}'  different  from  the 
siliceous  ones  except  as  influenced  by  the  greater  proportion  of  hematite 
present.  This  is  commonly  in  the  larger  grains  and  crystals,  although 
there  are  intermingled  with  them  some  of  the  small  transparent  plates.  In 
the  richer  bands  the  hematite  is  practically  in  solid  masses  of  snugl}^ 
compacted  granules.  In  many  instances  these  bauds  are  so  narrow,  so 
uniformly  parallel,  and  so  close  together  that  it  seems  as  though  the  ore 
must  have  been  infiltrated  along  bedding  cracks.  Indeed,  in  some  sections 
there  are  visible  cracks  into  which  ore  has  penetrated,  and  vein-like  streaks 
of  a  very  finely  granular  quartz  along  the  sides  of  which  are  narrow 
borders  of  hematite  and  limonite.  Sometimes  the  veins  enlarge  and 
inclose  small  ca-vities,  on  the  walls  of  which  there  are  likewise  thin  coat- 
ings of  hematite.  In  the  wider  ore  bands  the  ore  is  usually  denser  on  the 
sides  than  in  the  centers,  but  even  in  this  case  the  ore  is  rarely  sharply 
defined  from  the  jasper  through  which  it  cuts,  since  each  grades  into  the 
other  in  consequence  of  the  increase  in  the  quantity  of  one  of  their  con- 
stituents and  the  diminution  in  the  quantity  of  the  other. 

Some  of  the  specimens,  which  appear  homogeneous  when  examined 
megascopically,  are  found  to  be  minutely  brecciated  when  viewed  under 
the  microscope.     The  fractures  caused  by  the  brecciation  are  healed  by 


ALGONKIAN,  VULCAN  FORMATION.  341 

quartz.  Veinlets  of  the  same  substance  also  traverse  unbrecciated  speci- 
mens ill  different  directions,  but  most  frequently  parallel  to  the  bedding, 
and  small  veins  of  calcite  and  hematite  are  also  common.  In  the  straighter 
portions  of  the  quartz  veins  the  grain  of  the  vein  filling  is  nearly  of  the 
same  size  as  that  of  the  surrounding'  jasper,  but  in  curved  portions,  and 
particularly  in  the  triangular  areas  between  the  fragments  of  the  brecciated 
jaspers,  the  grain  of  the  quartz  filling  is  much  coarser.  From  the  great 
abundance  of  these  veins  it  is  clear  that  the  jaspilites  have  been  subjected 
to  silicification  processes  subsequent  to  the  silicification  which  gave  rise  to 
the  jasper. 

The  granular  or  sandy  jaspilites  are  more  varied  in  character  than  the 
flinty  varieties.  In  some  of  them  the  layers  of  jasper  seem  to  difter  little 
from  those  of  the  flinty  jasper  except  in  the  presence  of  a  few  apparently 
fragmental  quartz  grains  and  of  a  small  number  of  jasper  fragments.  The 
greater  part  of  the  rock  consists  of  the  usual  aggregate  of  interlocking  quartz 
grains,  hematite  particles,  and  here  and  there  a  scattered  magnetite  crystal. 
In  natural  light  the  quartz  mosaic  appears  entirely  uniform  in  structure, 
but  between  crossed  nicols  it  often  breaks  up  into  many  oval  or  rounded 
areas  composed  of  aggregates  of  a  few  or  many  small  grains  which  are 
distinctly  marked  off  from  the  surrounding  matrix  by  difi'erences  in  the 
size  of  their  grains.  In  some  cases  the  components  of  these  areas 
interlock,  while  in  other  instances  they  are  in  crushed  fragments. 
Although  no  definite  evidence  is  at  hand  to  confirm  the  view,  it  never- 
theless seems  probable  that  these  areas  represent  original  sand  grains  in  a 
sedimentary  rock.  Nearly  all  the  quartz  grains,  whether  in  the  rounded 
areas  referred  to  or  in  the  surrounding  matrix,  contain  great  numbers 
of  small  hematite  plates.  The  greater  part  of  this  mineral  is,  however, 
in  little  crystals  and  irregular  masses  between  the  grains.  In  nearly  all 
respects  the  iron  oxides  are  in  the  same  forms  and  they  exhibit  the  same 
relations  with  the  quartz  as  was  noted  in  the  case  of  the  ores  in  the  flinty 
jaspers.  As  in  the  latter  case,  the  ore  bands  are  simply  layers  in  which 
the  proportion  of  hematite  is  largely  in  excess  of  silica.  Sometimes 
magnetite  is  present  in  considerable  quantities,  in  certain  instances  in 
sufficient  quantity  to  impart  to  the  whole  rock  a  recognizable  magnetism. 
Occasionally  a  fragmental  grain  of  zircon  is  observed.  Besides  the 
constituents  already  mentioned  there  is  noticed  in  not  a  few  specimens  a 
finely  fibrous  aggregate  of  a  light-green,  very  feebly  polarizing   mineral. 


342  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

It  occurs  as  little  nests  scattered  between  the  quartz  grains  in  the  jasper 
bands  and  between  the  hematite  grains  in  the  ore  bands.  It  also  occupies 
the  central  portions  of  many  quartz  veins,  and  forms  rather  large  masses 
where  these  widen  out.  This  mineral,  which  is  probably  serpentine  or 
some  nearly  allied  species,  is  undoubtedly  an  infiltrated  substance  intro- 
duced after  the  rocks  had  assumed  nearly  their  present  character.  Calcite 
is  present  also  in  little  isolated  nests,  more  frequently  in  the  jasper  layers 
than  in  the  ferruginous  ores,  and  much  more  frequently  in  both  than  in  the 
corresponding  rocks  of  the  Traders  member.  In  some  specimens  a  little 
earthy  green  chloritic  substance  is  also  observable.  Quartz,  calcite,  and 
hematite  veins  cut  both  ore  and  jasper. 

The  greater  number  of  the  sandy  jaspilites  possess  a  very  beautiful 
oolitic  or  nodular  structure,  which  is  much  more  distinctly  apparent  in  the 
jasper  layers  than  in  the  ore  bands  (PI.  XIX,  C,  D).  It  is  due  partly  to  the 
prevalence  of  this  structure  that  these  rocks  are  more  granular  than  the 
other  jaspilites  of  the  district.  The  nodular  structure  has  ah-eady  been 
referred  to  in  the  description  of  some  of  the  beds  'of  the  Traders  member  (p. 
303).  It  is,  however,  so  very  much  more  common  in  the  Curry  jaspilites 
than  it  is  in  the  corresponding  Traders  rocks  that  it  may  well  be  considered 
the  characteristic  structure  of  the  former.  Only  rarely  can  the  structure  be 
recognized  in  the  hand  specimen  and  then  only  when  the  concretions  are 
composed  of  ore  lying  in  a  matrix  of  jasper.  In  thin  section,  however,  it  is 
seen  in  great  perfection.  Of  course,  all  traces  of  the  original  material  of  the 
concretions  have  disappeared,  but  there  remain  as  proofs  of  their  former 
existence  a  great  number  of  beautiful  pseudomorphs  composed  of  quartz  and 
hematite.  In  some  specimens  these  are  sparsely  scattered  through  a  ground- 
mass  with  the  features  of  the  nonoolitie  jaspers;  in  others  they  are  closely 
crowded  together,  constituting  more  than  three-fourths  of  the  rock  visible. 
In  the  majority  of  cases,  however,  the  nodules  are  present  only  in  certain 
bands  separated  from  one  another  by  bands  devoid  of  them,  as  though  the 
rock  had  been  composed  of  alternating  layers  of  oolitic  and  nonoolitie 
material. 

The  nodular  structure  is  best  studied  in  natural  light.  As  already 
related,  the  original  material  of  the  concretions  has  entirely  disappeared. 
It  is  now  represented  by  the  same  constituents  as  those  forming  the  matrix 
in  which  they  lie,  viz,  quartz  and  hematite.  The  quartz  is  usually  identical 
with  that  in  the  surrounding  matrix.     It  is  in  interlocking  grains  filled 


ALGONKIAN,  VULCAN  FORMATION.  343 

with  hematite  dust  and  abundant  hquid  inclusions.  As  a  general  thing 
the  coarseness  of  the  grain  is  the  same  in  the  nodules  as  in  the  matrix 
(see  PI.  XIX,  F),  but  occasionally  the  nodules  are  a  little  finer  grained. 
The  characteristic  feature  of  the  concretions  is  the  arrangement  of  the 
hematite.  This  mineral  usually  occurs  in  one  or  several  concentric  lines 
producing  circles,  ovals,  or  other  curved  forms,  inclosing  a  quartz  mosaic, 
which,  as  has  been  said,  is  identical  with  the  mosaic  outside  of  the  lines  (PI. 
XIX,  C,  D).  Sometimes  the  lines  are  continuous  and  thin,  often  they  are 
thick,  and  occasionally  the  ore  occupies  neai'ly  the  whole  area  of  the  nodule 
(PI.  XIX,  E).  In  other  cases  the  hematite  is  in  little  crystals,  arranged 
along  a  curved  line  indistinctly  outlining  an  area. 

When  viewed  between  crossed  nicols  the  entire  field  of  view  of  an 
oolitic  band  is  resolved  into  an  aggregate  of  small  quartz  grains,  broken 
here  and  there  by  opaque  ore  masses.  The  general  impression  produced  is 
that  of  a  practically  homogeneous  rock.  When  viewed  in  natural  light, 
however,  the  appearance  of  the  section  is  strikingly  different.  The  concre- 
tions stand  out  plainly  against  a  nearly  colorless  background  and  give  the 
impression  that  the  rock  is  composed  of  a  gi'eat  number  of  black-bordered 
sand  grains  of  a  uniform  shape  and  size  lying  in  a  quartzitic  groundmass. 
It  is  only  when  the  nicols  are  crossed  and  the  interiors  of  the  supposed 
grains  are  discovered  to  be  composed  of  an  aggregate  indistinguishable 
from  the  surrounding  matrix,  and  many  of  the  grains  of  this  aggTCgate 
are  found  to  be  continuous  with  grains  in  the  surrounding  mass,  that  this 
view  is  dispelled  and  the  ovals,  circles,  etc.,  are  recognized  as  sections  of 
concretions. 

Within  some  of  the  bands  the  concretions  are  elongated  and  arranged 
indiscriminately  with  their  longer  axes  in  any  direction,  but  usually  the 
elongated  forms  lie  with  their  long  directions  in  the  plane  of  the  bedding-. 
In  schistose  phases,  in  which  all  the  components  are  elongated,  the  nodules 
are  much  flattened  and  drawn  out  to  several  times  their  normal  lengths,  and 
often  their  quartz  components,  as  well  as  the  corresponding  constituents  of 
the  groundmass,  are  also  slightly  elongated  and  are  crossed  by  strain 
shadows.  The  ore  masses  are  also  often  drawn  out  to  great  lengths,  appear- 
ing as  lenticular  stringers  or  thin  bands  woven  in  and  out  between  com- 
posite lenses  of  quartz. 

Many  of  the  concretionary  masses  are  identical  in  all  essential 
respects  with  the   ore   concretions  observed  by  Van  Hise  and  Irving  in 


344  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

the  Gogebic  and  Gunflint  Lake  i-ocks,  and  by  Van  Hise  in  the  Marquette 
jaspiUtes."  Others  are  hke  those  observed  by  Leith  in  the  ferruginous 
cherts  of  the  Mesabi  area.  The  conci'etions  in  the  Gruniiint  Lake  beds 
are  shown  to  have  l^een  without  doubt  originally  nodules  of  siderite  in 
a  ferruginous  cherty  carbonate,  and  most  of  those  in  the  Gogebic  and 
Marquette  rocks  have  almost  as  certainly  been  shown  to  have  originated 
in  similar  concretions.  The  nodules  in  the  Mesabi  cherts  were  derived 
partly  from  siderite,  but  priucijjally  from  granules  of  a  magnesium 
iron  silicate  which  Leith  calls  greenalite.  Some  of  the  structures  in  the 
Menominee  jaspers  are  identical  with  those  pictured  in  the  report  on  the 
Penokee  series,''  but  the  concretions  difPer  from  most  of  those  illustrated  in 
tlie  Penokee  monog-raph  in  the  fact  that  no  original  siderite  or  other 
ferruginous  carbonate  has-  been  detected  in  them.  A  single  quotation  from 
a  description  of  the  ja.spers  in  the  Marquette  district  will  reveal  the  close 
similarity  in  appearance  between  the  concretionary  structure  in  these  rocks 
and  that  in  the  Menominee  jaspilites.  In  his  account  of  the  microscopical 
features  of  the  Negaunee  jaspers,  Van  Hise  writes:" 

In  the  jaspers  *  *  *  is  also  a  Ijeautiful  concretionary  structure  exactly 
similar  to  that  of  the  ferruginous  cherts  of  the  Penokee  district.  The  concentric 
zones  of  red  hematite,  separated  hy  a  greater  or  less  distance,  appear  as  if  painted 
upon  the  quartzose  background,  the  grains  of  which  seem  in  no  way  to  be  affected 
by  the  hematite.  *  *  *  In  some  slides  the  concretions  are  decidedly  flattened  by 
pressure. 

Except  for  the  statement  that  the  heuiatite  is  red,  this  desci-iption  will 
apply  word  for  word  to  many  of  the  Menominee  jaspers.  In  these,  however, 
the  hematite  is  generally  opaque. 

Most  of  the  nodules  in  the  Menominee  jaspers  are,  however,  more  like 
those  described  by  Leith  as  characteristic  of  altered  greenalite  rocks.  Some 
of  the  illustrations  published  by  this  author "*  might  easily  be  duplicated  in 
photographs  of  Menominee  jaspers. 

n  Irving,  Roland  Duer,  and  Van  Hise,  Charles  Richard,  The  Penokee  iron-bearing  series  of  Michigan 
and  Wisconsin;  Mon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  pp.  200-209  and  260-265.  Van  Hise,  Charles 
Richard,  and  Bayley,  William  Shirley,  The  Marquette  iron-bearing  district  of  Michigan,  with  atlas, 
including  a  chapter  on  the  Republic  trough  by  Henry  Lloyd  Smyth:  Mon.  V.  S.  Geol.  Survey,  vol. 
28,  1897,  pp.  373,  376. 

6Mon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  PI.  XXII,  tigs.  1  and  2,  PI.  XXVI,  figs.  1  and  2,  PL 
XXVIII,  flg.  2. 

cMon.  r.  S.  Geol.  Survey,  vol.  28,  1897,  p.  373. 

('Leith,  C.  K.,  The  Mesabi  iron-bearing  district  of  Minnesota:  Mon.  V.  S.  Geol.  Survey,  vol.  43, 
1903,  Pis.  XIV  and  XV,  A,  C,  and  D. 


ALGONKIAN,  VULCAN  FORMATION.  345 

Besides  the  masses  of  concretionary  origin  there  are  also  present  in 
many  of  the  Curry  sections  quartz  ovoids  that  are  not  outHned  by  rings  of  ore. 
These  are  distinguished  from  the  surrounding  matrix  by  the  fact  that  they 
are  very  fine  grained  and  that  their  material  is  filled  A^'ith  minute  particles 
of  dust.  They  are  thought  to  be  small  jasper  fragments  that  were  inter- 
mingled with  the  sediments  in  which  the  nodules  were  formed.  A  few 
small  fragments  of  quartz  with  the  usual  peripheral  enlargements  are  also 
met  with  in  some  specimens.  The  fragments  are  usually  composite,  though 
occasionally  a  homogeneous  one  is  discovered.  The  composite  character 
of  most  of  these  shows  conclusively  that  the  entire  rock  in  which  they 
occur  has  been  silieified,  and  that  even  the  quartz  of  which  these  fragments 
probably  consisted  was  dissolved  and  new  quartz  like  that  of  the  main 
body  of  the  rock  was  deposited  in  its  place.  Although  in  some  instances 
fragments  and  concretions  are  found  in  the  same  layer,  they  usually  occur 
in  different  layers,  separated,  perhaps,  by  a  thin  seam  of  ore.  One  layer 
may  consist  almost  exclusively  of  concretions  embedded  in  a  sparse  matrix, 
while  the  next  layer,  distant  only  a  small  fraction  of  an  inch,  may  l)e  made 
up  of  many  round  and  oval  quartz  grains  greatly  enlarged  by  additions  of 
quartz  in  optical  continuity  with  them,  some  homogeneous,  othei's  composite, 
and  all  embedded  in  an  abundant  fine-grained  jasper.  The  conditions  of 
deposition  must  have  varied  rapidly  to  give  rise  to  such  a  marked  difference 
in  sediments  within  such  short  vertical  distances. 

In  the  ore  bands  the  oolitic  structure  is  likewise  in  evidence,  but  here 
the  material  is  opaque  and  the  structure  is  much  more  difficult  to  recognize, 
especially  if  the  ore  is  very  dense.  In  the  less  dense  bands  the  ore  borders 
around  the  ovoids  are  much  thicker  than  those  around  the  concretions  in 
the  siliceous  bands,  and  in  many  instances  entire  concretions  consist  of  ore. 
Moreover,  ore  crystals  abound  within  the  concretions,  and  a  great  deal  of 
ore  occurs  in  the  interspaces  between  them.  A  sparse  quartz  matrix 
containing  an  occasional  jasper  fragment  lies  between  the  ore  masses.  In 
the  dense  ores  the  entire  matrix  is  replaced  by  hematite;  but  even  in  these 
a  nodular  structure  is  revealed  on  the  edges  of  the  section  where  the  grinding 
has  caused  the  ore  to  split  along  curved  lines  into  round  and  oval  masses 
like  the  concretions  in  the  jaspers. 

The  slaty  varieties  of  the  Curry  member  do  not  differ  as  much  from 
the  flinty  and  sandy  or  granular  varieties  as  might  be  inferred  from  an 


346  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

examination  of  hand  specimens  alone.  In  composition  and  structure  they 
are  gradation  phases  between  the  Brier  slates  and  the  normal  phases  of  the 
more  siliceous  portions  of  the  jaspilites,  always  approaching  more  closely 
the  jaspers  than  the  slafes.  Some  of  the  samples  which  in  the  hand 
specimen  present  the  appearance  of  only  slightly  altered  slates  are  found  to 
be  entirely  changed  to  jaspers.  In  spite  of  the  fact  that  they  retain  in  great 
perfection  the  definite  banding  and  the  characteristic  texture  of  the  slates, 
they  have  been  very  completely  silicified.  All  fragmental  material  has 
disappeared  and  the  rocks  are  now  completely  crystalline.  Many  of  the 
specimens  afford  excellent  illustrations  of  the  manner  in  which  a  rock  may 
be  entirely  changed  by  the  replacement  of  its  original  components,  while 
still  retaining  its  fundamental  structures. 

The  most  jasper-like  varieties  of  these  rocks  differ  but  little  from  the 
normal  jaspers  in  their  essential  features  except  that  they  contain  more 
chlorite.  The  varieties  most  like  the  Brier  slates  differ  from  these  rocks  in 
possessing  a  grouudmass  of  crystalline  quartz  in  place  of  the  fine  fragmental 
groundmass  of  the  slates.  Moreover,  the  smaller  fragments  have  been 
entirely  replaced  by  a  fine-grained  aggregate  of  interlocking  quartz. 

The  intermediate  phases  present  a  greater  individuality,  though  even 
these  do  not  differ  markedly  from  the  jaspilites.  They  are  characterized  by 
the  presence  of  a  great  abundance  of  light-green  chlorite  in  plates  and  in 
aggregates  of  tiny  fibers  in  the  jasper  layers,  and  by  the  presence  of  plates 
and  small  iiakes  of  a  darker-green  chloritized  biotite  in  the  ore  layers.  The 
chlorite  occurs  in  the  interspaces  between  neighboring  quartz  grains  and 
the  biotite  plates  between  the  magnetite  grains  and  usually  attached  to 
them.  The  small  biotite  flakes  are  scattered  through  the  quartz  grains.  In 
most  specimens  a  brown  or  reddish-brown  ocher  is  also  very  common. 
It  appears  as  an  irregular  coating  on  the  quartz  grains,  as  small  masses 
between  them,  and  as  little  radial  groups  sometimes  within  and  sometimes 
between  them.  It  is  especially  abundant  in  some  of  the  hematite  layei's, 
constituting  a  large  proportion  of  the  mass  in  which  the  ore  particles  are 
embedded.  In  all  instances  it  seems  to  be  a  decomposition  product  of 
chlorite. 

The  ore  bands  are  usually  not  unlike  the  siliceous  bands  except  in  the 
possession  of  a  large  quantity  of  hematite  and  in  the  presence  of  a  chlorit- 
ized biotite  in  place  of  the  chlorite  of  the  jaspers.  In  a  few  distinctly  slaty 
ores  the  rock  is  practically  a  sandstone  with  a  quartz-hematite  cement. 


ALGONKIAN,  VULCAN  FORMATION.  347 

It  consists  of  numberless  enlarged  quartz  grains,  a  few  cloudy  masses 
that  look  like  decomposed  feldspar  fragments,  and  a  few  small  masses  and 
plates  of  chlorite  surrounded  by  an  aggregate  of  opaque  and  transparent 
hematite  and  quartz.  In  this  cement  the  hematite  predominates  to  a  very 
large  degree  over  the  quartz,  the  latter  seemingly  occurring  merely  as  a 
filling  of  little  spaces  in  a  porous  aggregate.  Many  of  the  quartz  grains 
show  strain  shadows. 

In  the  preceding  paragraphs  repeated  reference  has  been  made  to  the 
fact  that  many  specimens  of  the  Curry  rocks  contain  calcite  or  some  other 
carbonate.  Usually  the  mineral  is  uniformly  distributed  in  small  quan- 
tities between  the  quartz  grains  of  the  jasper  bands,  but  sometimes 
it  occurs  in  very  considerable  masses  both  in  the  jasper  and  the  ore, 
and  occasionally  in  series  of  little  nests  nearly,  but .  not  quite,  connecting 
with  one  another  along  lines  parallel  to  the  bedding.  Distinct  calcite 
veinlets  are  also  sometimes  met  with  The  characters  and  distribution  of 
the  mineral  leaves  no  doubt  that  its  origin  was  subsequent  to  that  of  the 
major  portion  of  the  rocks.  It  was  infiltrated  after  the  rocks  attained 
ajoproximately  their  present  condition  and  crystallized  in  pores  and  crevices 
that  already  existed,  or  that  were  made  by  the  removal  of  some  other 
component.  No  oi'iginal  carbonate  has  been  found  in  any  of  the  Curry 
rocks.  The  material  that  was  referred  to  as  original  siderite  in  the  prelimi- 
nary report  on  the  district,  upon  closer  stud}^  is  discovered  to  be  a  secondary 
carbonate. " 

The  rocks  containing  carbonate  in  greatest  amount  are  those  in  the 
workings  and  the  immediate  vicinity  of  the  Curry  nfine.  In  addition  to 
the  large  masses  and  veins  of  red  dolomite  that  have  already  been  men- 
tioned as  being  conspicuous  in  the  Curry  ores  and  jaspilites  the  rocks  con- 
tain also  dolomitie  material  which  is  I'evealed  only  by  the  microscope.  In 
these  phases  of  the  rocks  the  carbonate  has  almost  completely  replaced  the 
quartz.  Nearly  all  the  silica  that  was  probably  once  present  has  dis- 
appeared and  in  its  place  is  a  coarse  aggregate  of  dolomite  in  which  magne- 
tite crystals  and  hematite  plates  and  grains  are  embedded  in  the  same 
manner  as  they  exist  in  the  siliceous  ores  and  jaspilites  elsewhere.  In 
most  specimens  much  of  the  entire  portion  of  the  section  in  the  field  of  view 
at  any  one  time  is  occupied  by  a  continuous  mass  of  carbonate  that  polar- 

nGeologic  Atlas  U.  S.,  folio  62,  U.  S.  Geol.  Survey,  1900,  p.  ^. 


348 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


izes  uniformh-.  In  the  cases  where  the  beds  are  Ijrecciated  the  carbonate 
cemeuts  the  fragments  together.  In  extreme  cases  both  fragments  and 
cement  are  carbonated.  The  brecciated  structm-e  remains,  but  all  the  origi- 
nal components  except  the  ores  have  been  replaced  by  the  carbonate.  In 
some  portions  of  a  few  sections  the  ore  is  in  round  and  circular  masses  and 
in  concentric  rings  that  look  like  pseudomorphs  of  nodules;  but  these  also 
are  carbonated,  nothing  remaining  of  their  original  components  but  the  oi'es. 

It  is  quite  evident  that  these  rocks  have  been  completely  permeated  by 
carbonate-bearing  solutions,  and  that  these  solutions  have  carried  off  all 
the  silica  and  chlorite  that  was  originally  in  the  rocks  and  deposited  a 
dolomitic  carbonate  in  their  place.  That  none  of  this  carbonate  was  an 
original  component  of  the  rock  in  its  present  position  is  apparent  without 
discussion. 

The  identification  of  the  carbonate  as  dolomite  is  confirmed  by 
analyses  of  the  ore  from  the  Curry  mine  furnished  by  Mr.  F.  A.  Janson, 
engineer  of  the  Peuu  Iron  Mining  Company.  Analysis  I  is  of  the  ore 
obtained  from  the  Curry  member,  and  II  that  of  an  ore  taken  from  the 
Traders  beds. 

Analyses  of  carbonated,  ores  from  Curry  mine. 


I. 

II. 

Fe,0,                                        

73.41 

.62 

.89 

3.42 

11.59 

10.61 

68.04 

A1„0,                                     - 

1.41 

MnOj                                          

1.04 

SiOj                                             

11.72 

CaCOa                                        

CaO  =      4. 91 

aTctCO.                                                                       -           

MgO=      5. 41 

COj  =      7.31 

Total                           

100.54 

99.84 

In  the  first  sample  the  calcium  and  magnesium  carbonates  constitute 
about  22  per  cent  of  the  ore,  and  in  the  second  about  15  per  cent.  In  the 
first  the  two  carbonates  are  nearly  in  the  proportion  demanded  for  typical 
dolomite  of  the  formula  (CaMg)C03,  which  would  require  12.63  per  cent 
of  CaCOg  to  lO.b'l  per  cent  MgO.  If  all  the  CaO  in  the  second  analysis 
is  present  as  CaCOs,  the  proportion  of  the  two  carbonates  in  the  ore  is  6.59 
MgCOg  and  8.77   CaCOs.     Typical  dolomite  would  require  7.36  MgCOa  to. 


ALGONKIAN.  VULCAN  FORMATION.  349 

8.77  CaCOg.  It  is  therefore  quite  certain  that  the  carbonate  which  replaces 
the  siUca  in  these  rocks,  hke  that  which  saturates  the  Brier  slates  near  by 
(see  p.  328),  is  almost  a  pure  dolomite  of  the  type  CaCOg  +  MgCOg. 

RELATIONS   BETWEEN    THE    MEMBERS   OF   THE    VULCAN    FORMATION. 

Where  no  marked  disturbances  exist  between  the  Traders  member  and 
the  Brier  slates,  the  first  grades  into  the  second  by  diminution  of  the  amount 
of  ferruginous  material  and  increase  in  the  proportion  of  slaty  material. 
At  the  same  time  there  is  a  diffusion  of  the  quartzose  component  and  the 
gradual  disappearance  of  the  distinctively  quartzose  layers.  The  silica, 
moreover,  changes  from  the  crystalline  variety  characteristic  of  the  jaspers 
to  the  plainly  clastic  quartz  characteristic  of  slates.  When  the  ferruginous 
material  is  much  reduced  in  quantity  and  the  fragmental  comjionents  are 
correspondingly  increased,  the  ore-bearing  Traders  bed  becomes  the  Brier 
slate.  This  gradation  occupies  only  a  very  short  vertical  range,  so  that 
the  line  between  the  Traders  member  and  the  Brier  slate  is  usually  deter- 
minalile  within  a  few  feet. 

Where  marked  disturbances  have  occurred,  as  in  the  vicinity  of  Nor- 
way and  eastward  for  several  miles,  the  relations  between  the  two  members 
are  very  different.  Wherever  it  can  be  seen,  the  contact  between  the 
Traders  and  Brier  members  is  sharp.  In  many  places  the  contact  seems  to 
be  slickensided  and  often  to  be  a  plane  of  differential  movement.  At  the 
open  pits  of  the  Norway  and  the  Cyclops  mines  and  those  north  of  the 
Curry  mine,  and  between  this  mine  and  the  West  Vulcan,  the  Traders 
rocks  are  in  places  pseudoconglomeratic.  The  Brier  slates  also  may  be 
brecciated  (PI.  XXI,  ui  and  B).  Moreover,  the  brecciation  is  not  confined 
to  these  two  members,  but  the  underlying  dolomite  is  at  some  places  likewise 
brecciated  for  a  short  distance  beneath  its  upper  surface.  The  phenomena, 
wherever  studied,  appear  to  indicate  that  the  relations  between  the  dolo- 
mite, the  Traders  member,  and  the  Brier  slates  were  originally  normal,  i.  e., 
the  ore-bearing  beds  were  principal!}'  detrital  material  lying  upon  tlie  dolo- 
mite, and  that  the  Brier  slates  were  conformable  deposits  ujjon  the  ferru- 
ginous beds.  At  the  time  of  folding  slipping  occuired  along  the  contact 
between  the  Up^jer  Menominee  series  and  the  Lower  Menominee  series 
and  between  the  Traders  and  Brier  members.  The  dolomite  was  brecciated 
to  some  extent,  the  Traders  detrital  ores  were  crushed  and  brecciated,, and 


s 


350  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

in  several  instances  the  lower  portions  of  the  Brier  slates  were  likewise 
included  within  the  zone  of  movement  and  were  fractured  and  brecciated. 
Talc  and  serpentine  were  developed  along  the  slickensided  surfaces  and 
were  deposited  in  joint  cracks  and  openings  made  in  the  rocks,  and,  later, 
the  breccias  were  enriched  by  the  deposition  of  hematite  and  other  iron 
comjiounds.  Thus  both  the  Traders  member  and  the  lower  part  of  the 
brecciated  Brier  slates  became  sufficiently  ferruginous  to  Avarrant  mining. 
This  line  of  contact  is  marked  by  large  open  pits  in  the  southeast  quarter 
of  sec.  5  and  the  northeast  quarter  of  sec.  9,  T.  39  N.,  R.  29  W.  The  ore 
belonging  to  the  Traders  member  was  taken  from  them  some  years  ago. 
But  it  was  not  until  the  summer  of  1899  that  the  demand  for  lean  ores  was 
so  great  that  the  ferruginous  phases  of  the  Brier  slates  could  be  mined  with 
profit.  In  this  year,  however,  some  of  the  Norway  mine  product  consisted 
of  this  material. 

From  the  descriptions  (if  these  jDits  given  in  the  Tenth  Census  reports" 
it  maybe  inferred  that  at  the  time  the  pits  were  visited  (1880)  the  relations 
of  the  breccias  to  the  ores  now  mined  out  could  be  easily  seen.  The  entire 
Traders  member  was  evidenth'  not  brecciated,  for  there  were  distinct  bands 
of  sjjecular  and  slaty  ores  near  the  foot  walls  of  pit  No.  3  (West  Vulcan), 
and  at  various  places  in  the  Perkins,  the  Baginaw  (afterwards  north  portion 
of  the  Perkins  pit),  the  Norway,  and  the  Cyclops  pits.  Since  the  rock 
forming  the  walls  of  the  pits  is  brecciated  on  the  strike  of  the  naaterial  that 
has  been  removed,  which  was  presumably  ore,  it  seems  jjrobable  that 
pockets  of  nonbrecciated  ore  actually  existed  in  the  midst  of  the  breccias. 
They  may  have  been  finely  comminuted  breccias  which  were  so  completely 
ferruginized  that  all  of  their  original  components  disappeared,  and  which 
later,  hj  slight  movements,  became  schistose  and  lost  their  brecciated 
structure.  In  other  words,  the  same  conditions  seem  to  have  controlled 
the  deposition  of  the  ore  in  the  breccias  as  elsewhere.  While  the  entire 
brecciated  zone  was  enriched-,  certain  portions  of  it,  being  more  crushed 
than  (Others,  gave  rise  to  the  richest  ores. 

The  change  from  the  Brier  slates  to  the  Curry  member  proceeds  in 
the  opposite  manner  from  that  of  the  Traders  member  into  the  Brier 
member.  The  argillaceous  constituent  diminishes,  the  quartzose  com- 
ponent becomes  aggregated  into  bands  and  at  the  same  time  loses  its 
fragmental    character    and    becomes    crystalline    or    cherty,    ferruginous 

"Reports  of  the  Tenth  Census,  vol.  l.i,  1886,  pp.  441-447. 


ALGONKIAN,  VULCAN  FORMATION.  351 

material  is  introduced,  and  hematite  increases  in  abundance  and  becomes 
segregated  into  distinct  layers.  Sometimes  the  gradation  is  sudden, 
occupjnng  but  a  foot  or  more;  sometimes  it  is  more  gradual.  Jasper 
layers  appear  in  the  slates  10  feet  or  more  from  the  fully  developed  beds 
of  the  Curry  member.  These  increase  in  number  and  thickness  as  higher 
horizons  are  reached.  The  interlaminated  slates  grow  more  ferruginous  and 
lose  their  fragmental  texture,  hematite  is  introduced  along  their  bedding 
planes,  and  finally  the  slaty  layers  are  transformed  into  lean  ores.  Thus 
typical  jaspilites  are  produced.  The  transition  can  be  seen  at  a  number 
of  places  on  the  surface  and  at  many  more  in  the  underground  workings 
of  the  mines.  In  the  mine  workings  the  transition  is  often  so  sudden  that 
there  is  no  difficulty  in  drawing  a  sharp  line  between  the  two  sets  of  beds. 
On  the  surface  the  case  is  somewhat  different,  since  weathering  oftentimes 
masks  the  characteristic  features  of  the  slates  and  causes  them  to  resemble 
the  Curry  rocks.  At  the  Curry  shaft  No.  1,  in  the  south ^^^est  quarter  of 
the  northeast  quarter  of  sec.  9,  T.  39  N.,  R.  29  W.,  the  transition  is  seen  to 
occur  laterally  as  well  as  vertically.  At  this  place  is  an  excavation  in  the 
hillside  exposing  the  upper  portion  of  the  Brier  slates  and  the  lower  portion 
of  the  Curry  member.  The  north  side  of  the  excavation  is  bordered  by 
slates.  On  its  west  side  the  vertical  gradation  between  the  slates  and  the 
iron-bearing  beds  can  be  profitably  studied.  It  exhibits  the  gradation  by 
means  of  the  interposition  of  jasper  bands  described  above.  On  its  east 
side,  only  200  feet  distant  from  the  west  side,  the  rocks  are  principally 
well-defined  beds  of  the  Curry  member.  Since  no  evidences  of  folding 
except  slight  plication  can  be  detected  in  any  of  the  rocks,  and  since  the 
jaspilites  are  on  the  direct  strike  of  the  slates  on  the  west  side  of  the  cut  the 
inference  that  there  is  also  a  horizontal  gradation  here  is  unavoidable. 

At  one  or  two  places  the  contact  between  the  two  series  is  extremely 
sharp,  no  transition  of  any  kind  being  observable.  In  most  of  these 
instances  there  is  plainly  a  small  fault  between  the  two  sets  of  beds.  Such 
are  the  conditions  on  the  fourth  level  of  the  Pewabic  mine,  on  the  sides  of 
some  of  the  pits  of  the  Cyclops,  Curry,  and  West  Vulcan  groups  of  excava- 
tions, and  more  particularly  in  the  dividing  wall  between  the  pit  in  which 
No.  4  shaft  of  the  West  Vulcan  mine  is  situated  and  the  pit  to  the  west  of 
this  one  (see  map,  PI.  XXXIII). 

No  stratigraphical  break  has  been  discovered  anywhere  within  the 
Vulcan  formation. 


352  THE  MENOMINEE  IRON-BEAKING  DISTRICT. 


GENESIS. 


From  the  descriptions  of  the  various  members  of  the  Vulcan  formation 
that  have  been  given  it  is  evident  that  this  formation  comprises  a  series  of 
sediments  laid  down  in  water  in  successive  beds  from  bottom  to  top.     The 
bottom  layers  are  slates  and  coarse  quartzites  or  conglomerates,  composed 
laro-elv   of   waterworn    quartz    grains    and    fragments    of  jasper  and  ore. 
Plainlv  these  layers  are  mainly  fragmental  sediments  derived  from  a  pi-e- 
existing  land  surface.     The  slates  were  laid  down  at  some  distance  from 
the  shore  line  and  were  derived  from  a  land  surface  which  at  the  time  of 
their  deposition  consisted  largely  of  dolomite.     The  quartzites  and  con- 
o-lomerates  were  deposited  nearer  the  coast.     They  were  derived  from  a 
land  surface  composed  partly,  at  least,  of  jaspilites,  quartzites,  and  crystal- 
line rocks.     The  absence  of  coarse  conglomerates  indicates  that  the  deposits 
now  exposed  were  formed  at  some  distance  from  the  shore  line  rather  than 
aloiio-  beaches.     Currents  or  waves  caused  a  sorting  of  the  sediments  and 
produced  interlaminations  of  hematitic  and  quartzose  layers.     The  crystal- 
line quartzose  cement  in  the  quartzites  and  the  conglomerates,  and  the 
nodules  of  ore  in  the  latter  rocks  suggest  that  there  was  deposited  with  the 
frao-mental  material  some    of  the  ferruginous  carbonate   and  greenalite" 
nodules  which  at  higher  horizons  gave  rise  to  the  jaspers  of  the  jaspilites. 
If  this  is  so,  as  it  seems  to  be,  the  Vulcaii  epoch  was  ushered  in  by  condi- 
tions favorable  to  the  accumulation  of  fragmental  sediments  at  the  bottom  of 
a  sea  or  Iju)-  that  was  depositing  a  cherty  ferruginous  carbonate  or  silicate, 
or  both.     Thus,  in  the  lower  portion  of  the  Traders  member  clastic  and 
chemical  sediments  were  intermingled,  with  the  former  largely  in  excess. 
In  the  course  of  time,  probabl}'  after  the  district  was  folded,  the  slates  were 
altered  and  much  talc  and  serpentine  were  deposited  in  them,  partly  by  cir- 
culating waters  emanating  from  the  underlying  dolomite    and    probably 
]5artly  in  consequence  of  changes  set  up  in  the  dolomitic  material  of  the 
slates  themselves.     The  cherty  ferruginous  cement  of  the  quartzose  layers 
was  changed  to  a  crystalline   quartz  and    liematite  and  the  layers  were 
enriched  by  deposits  of  hematite  between  the  original  grains.    With  deepen- 
ing of  the  water  in  which  the  deposits  were  being  laid  down  these  became 
finer  grained.     The  proportionate  quantity  of  the  ferruginous  compounds 
precipitated  was  increased  and  the  series  of  mixed  mechanical  and  chemical 

"  For  theory  as  to  deposition  of  greenalite  see  Mon.  U.  S.  Geol.  Survey,  vol.  43,  1903,  pp.  247-259. 


ALGONKIAN,  VULCAN  FORMATION.  353 

sediments  grew  to  a  considerable  thickness.  In  some  places  and  at  certain 
horizons  the  deposits  were  almost  purely  chemical.  At  other  places  the 
mechanical  sediments  were  in  great  excess.  In  most  places  the  two  kinds 
of  sediments  were  precipitated  together.  There  thus  resulted  the  Traders 
series  of  beds,  consisting  of  alternating  layers  of  carbonates,  greenalite, 
ferruginous  and  quartzose  sands,  and  mixtures  of  the  three. 

The  conclusions  as  to  the  existence  of  original  carbonate  and  greenalite 
in  the  Vulcan  formation  is  based  principally  on  the  analogy  that  exists 
between  the  character  of  the  iron-bearing  beds  in  the  Menominee  district 
and  that  of  similar  beds  in  the  Marquette,  the  Gogebic,  and  the  Mesabi 
districts,  which  have  been  shown  to  have  developed  either  from  cherty 
ferruginous  carbonate  or  from  deposits  of  greenalite.  The  conclusion  is 
confirmed  by  the  presence  of  hematite  and  jasper  pseudomorphs  after  con- 
cretions and  nodules  in  the  rocks  of  the  Traders  member,  and  more  particu- 
larly in  those  of  the  Curry  member  of  the  Vulcan  series,  and  by  the  existence 
of  the  ores  in  the  Menominee  district  in  just  such  situations  as  are  demanded 
by  the  assumption  that  they  were  concentrated  by  descending  waters  (see 
p.  396). 

Since  the  steps  in  the  theory  that  derives  the  jaspilites  from  a  ferru- 
ginous carbonate  were  worked  out  mainly  by  Van  Hise  in  his  studies  on 
the  Gogebic,  the  Gunilint  Lake,  and  the  Marquette  districts,  we  can  do  no 
better  than  quote  his  statements  concerning  the  origin  of  the  jaspilites  in 
general,  as  explaining  the  mode  by  which  the  iron-bearing  beds  in  the 
Menominee  district  finally  came  to  have  their  present  characters.  With 
respect  to  the  origin  of  the  iron  in  the  carbonates,  he  writes :" 

When  the  individual  districts  are  taken  up,  it  will  be  seen  that  a  greenstone, 
often  ellipsoidal,  in  many  places  porous  and  amygdaloidal,  in  many  places  schistose 
and  rich  in  iron,  is  the  most  characteristic  rock  of  the  Archean,  and  that  similar 
rocks  occur  abundantly  in  the  Huronian.  Where  these  igneous  rocks  were  adja- 
cent to  the  seas  they  would  be  leached  by  the  underground  water  and  the  iron  trans- 
ported to  the  adjacent  seas.  It  is  possible  that  to  some  extent  this  leaching  process 
also  went  on  below  the  waters  of  the  sea.  The  iron  was  probably  transported  to  the 
water  mainly  as  carbonate,  but  to  some  extent  as  sulphate.  The  carbonate  would 
there  be  thrown  down  by  oxidation  and  hydration  as  limonite,  and  the  sulphate  in 
part  as  basic  ferric  sulphate.  Much  of  the  sulphate  was  probably  directly  precipi- 
tated as  sulphide  by  the  organic  material.     The  limonite  would  be  mingled  with  the 

"Van  Hise,  C.  R.,  The  iron-ore  deposits  of  the  Lake  Superior  region:  Twenty-tirst  Ann.  Kept. 
U.  S.  Geol.  Survey,  pt.  3,  1901,  pp.  319-322. 

MON  XLVI — 0-4 23 


354  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

organic,  matter,  which  was  undoubtedlj'  present,  as  shown  l)y  the  associated  carbon- 
aceous and  graphitic  shales  and  slates.  When  deepl}'  buried  the  organic  matter 
would  reduce  the  iron  sesquioxide  to  iron  protoxide.  By  the  simultaneous  decom- 
position of  the  organic  matter  carbon  dioxide  would  he  produced,  which  would  unite 
with  much  of  the  protoxide  of  iron,  producing  iron  carlionate.  The  sulphate  of  the 
basic  ferrous  sulphate  would  be  reduced  to  the  sulphide  b}'  the  organic  material, 
thus  producing  the  pyritic  carbonates.  Where  the  iron  was  brought  to  the  water 
mainly  as  sulphate,  the  direct  reduction  of  this  salt  by  organic  matter  would  form 
iron  sulphide  with  little  or  no  carbonate.  Simultaneously  with  the  production  of 
these  substances  chert  was  formed,  probably  through  the  influence  of  organisms." 
Some  of  this  silica  would  unite  with  a  part  of  the  iron  protoxide,  producing  ferrous 
silicate.  More  or  less  mechanical  sediment  would  also  be  laid  down.  Thus  the 
original  rocks — the  cherty  iron  carbonates,  the  ferrous  silicate  rocks,  and  the  pyritic 
cherts — would  be  produced.     *     *     * 

The  alterations  of  the  original  rocks  of  the  iron-bearing  formations  have  been 
along  two  general  lines,  depending  upon  whether  the  iron-bearing  carbonate  or 
ferrous  silicate  or  pyrite,  when  altered,  was  at  the  surface  or  at  considerable  depth. 
Where  the  rocks  were  altered  at  or  near  the  surface,  so  that  oxygen-bearing 
waters  were  abundant,  ferruginous  slates,  ferruginous  cherts,  and  ore  bodies  were 
produced.     *     *     * 

The  formation  of  the  ferruginous  slates  and  ferruginous  cherts  from  the  iron- 
bearing  carbonate  is  usually  a  process  of  liberation  of  carbon  dioxide  and  of  oxidation 
and  hydration  of  iron.  Where  oxidation  takes  place  with  little  h^-dration,  jaspilites 
may  be  formed.  *  *  *  Ordinarily  the  rearrangement  of  the  iron  and  chert 
emphasized  the  original  sedimentary  banding.     *     *     * 

For  the  development  of  jaspilite  further  alterations  are  commonlj'  required. 
The  first  stage  ordinarily  forms  ferruginous  slate  or  ferruginous  chert  at  or  near  the 
surface,  as  above  described.  These  rocks,  when  later  deeply  buried  by  sedimentation 
and  subsequently  folded,  are  altered  in  the  deep-seated  zone  in  which  dehydration  is 
one  of  the  characteristic  reactions.  The  h^^drated  iron  oxides  of  the  ferruginous 
slates  and  ferruginous  cherts  are  changed  to  hematite.  This  gives  the  rocks  the 
blood-red  appearance  of  jasper.  The  jaspilites  therefore  differ  mainly  from  the 
ferruginous  slates  and  the  ferruginous  cherts  in  the  nonh3'drated  condition  of  the 
iron  oxide. 

During  any  of  the  above  processes  of  alteration  the  iron  oxides  may  be  more  or 
less  concentrated.  The  concentration  may  result  in  bands  of  nearly  pure  iron  oxide 
between  the  leaner  portions  of  the  rock.  It  may  result  in  the  concentration  of  the 
iron  oxide  in  veins.  It  may  result  in  the  concentration  of  the  iron  oxide  in  large 
masses  under  peculiar  conditions,  as  fully  explained  below,  and  thus  produce  ore 
bodies.     The  ores  are  mainly  somewhat  hydrated  hematite,  but  limonite  and  anhydrous 


a  Van  Hise,  C.  R.,  The  Penokee  iron-bearing  series  of  ^Michigan  and  Wisconsin:  ^lon.  U.  S.  Geol. 
Survey,  vol.  19,  1892,  pp.  246-253.  Walcott,  C.  D.,  Fossil  Medusw:  Mon.  U.  S.  Geol.  Survey,  vol.  30, 
1898,  pp.  17-21. 


ALGONKIAN,  VULCAN  FORMATION.  355 

hematite  feither  ^irthy  or  speciilar)  occur  plentifully.  Magnetite  is  also  found.  Imt 
is  veiT  subordiiiate  in  quantity.  The  great  mass  of  the  iron  ore  of  the  Lake  Superior 
region  is  iron  sesquioxide." 

After  the  Traders  beds  had  been  laid  down  to  a  thickness  of  several 
hundred  feet,  conditions  ag'ain  changed,  the  cherty  carbonate  and  greenalite 
ceased  to  be  precipitated  and  the  deposits  for  a  time  consisted  exclusively 
of  mechanical  detritu.s  from  the  neighboring  shores.  This  was  comparatively 
fine  'grained,  and  consequently  must  have  accumulated  at  some  distance 
from  land.  It  consisted  of  the  debris  from  ciystalline  rocks,  among  which 
■were  many  that  were  basic.  What  the  nature  of  the  change  was  that 
■determined  the  cessation  of  chemical  precipitation  can  not  be  told.  Changes 
in  the  water  level  may  have  contributed  to  the  result.  Depression  of  the 
land  may  have  reduced  the  rate  of  erosion  of  the  basic  rocks  considered 
by  Van  Hise  to  be  the  source  of  the  iron  salts  and,  consequently,  the 
■amount  of  ferruginous  material  leached  from  them. 

At  the  end  of  Brier  time  the  conditions  that  prevailed  during  the  latter 
part  of  Traders  time  returned  and  the  chemical  precipitates  were  again 
deposited,  this  time  without  much  admixture  of  fragmental  detritus.  The- 
abundance  of  conci-etionary  ore  In  the  Curry  beds  shows  that  some  of  thes& 
'Consisted  largely,  if  not  almost  exclusively,  of  the  chemical  precipitate,, 
interbedded  perhaps  with  a  few  thin  layers  of  quartz  and  hematite  sand. 

In  the  course  of  time  the  ferruginous  jjrecljiltates  were  changed  to  hem- 
atite, the  silica  was  rearranged,  and  jasper  was  formed.  Where  the  Iron 
eomjjounds  were  in  beds  of  notable  thickness  the  resultant  jasper  Is  Impor- 
tant. Some  new  hematite  was  deposited  In  thin  layers  along  the  bedding' 
planes.  Another  portion  of  the  newly  formed  hematite  remained  or  was 
deposited  along  the  grains  of  the  detrital  ores,  thus  em-Ichlng  them,  espe- 
cially In  the  bottom  of  the  folds  and  In  areas  of  disturbance.  In  spite  of 
the  enrichment  of  the  Curry  member  in  Iron  oxide.  Its  ores  are  never- 
theless not  profitably  worked  at  as  many  places  as  are  those  of  the  Traders 
member.  The  ferruginous  detritus  In  the  Curry  beds  Is  usually  not  so  rich 
In  Iron  oxide  as  that  found  at  the  Traders  horizon.  Where  folds  exist  in  the 
member,  furnishing  favorable  situations  for  rich  deposits,  the  ore  bodies  may 
be  large  enough  and  rich  enough  to  warrant  mining,  but  for  the  greater 
part  of  its  extent  the  member  yields  only  lean  ores. 


n  For  a  discussion  of  the  chemical  changes  that  resulted  in  the  production  of  jaspilite  from  greena- 
lite, see  Mon.  U.  S.  Geol.  Survey,  vol.  43,  1903,  pp.  255-259. 


356  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

FOLDING. 
FOLDS  OF  LOWER  ORDERS. 

The  Vulcan  formation,  where  it  is  known  to  exist,  occupies  a  position 
on  the  upper  sides  of  the  dolomite  anticlines.  Its  major  folds,  or  folds  of 
the  first  order,  correspond  exactly  to  the  major  folds  of  the  Randville 
dolomite.  The  folds  of  the  second  order  correspond  also  with  those  of 
the  dolomite  (see  p.  237).  Within  the  formation  there  are,  moreovei', 
numerous  still  smaller  folds  of  the  third  order,  which,  because  of  the 
Jiardness  of  tlie  rocks  and  the  perfection  of  their  banding,  are  well 
<exliibited.  These  small  folds  may  be  observed  at  nearly  every  place  where 
raining  has  progressed  to  any  considerable  extent  and  at  many  other  places 
where  only  lean  ores  have  been  developed.  The  folds  of  the  third  order 
pitcli  in  the  same  direction  as  those  of  the  second  order,  on  which  they  are 
■superimposed,  but  the  strikes  of  their  axes  may  diverge  slightly.  Usually 
these  folds  are  directly  related  to  folds  of  a  coiTesponding  order  in  the 
■dolomite,  as  in  the  Aragon  mine  and  in  the  Norway  syncline,  but  often  they 
are  apparentlv  independent  of  the  folding  in  the  underlying  rock.  The 
minor  folds  are  extremeh"  important  guides  to  the  discovery  of  ore  bodies. 
The  folds  of  the  second  order  detennine  the  general  position  of  the  ore 
bodies,  while  the  folds  of  the  third  order  determine  in  many  cases  their 
more  exact  positions  within  the  larger  folds.  The  folded  slates  of  the 
formation  are  relatively  impervious,  and  where  not  shattered  often  furnished 
troughs  into  which  the  circulating-  waters  were  conveyed  and  the  oi'e 
deposits  formed.  In  exploring  operations  it  is  important  to  detennine  the 
strikes  and  dips  of  the  axes  of  the  minor  fokls,  not  only  because  they 
indicate  the  direction  of  the  pitch  and  strike  of  the  larger  folds,  but  also 
because  they  direct  attention  to  those  places  at  which  oi'e  bodies  are  most 
apt  to  exist. 

FOLDS  OF   HIGHER   ORDERS. 

In  addition  to  the  three  orders  of  folds  above  refeiTed  to,  there  may  in 
many  places  be  discovered  still  smaller  folds.  These  are  superimposed  on 
the  folds  of  the  third  order  in  the  same  way  in  which  the  latter  are  super- 
imposed on  the  folds  of  the  second  order.  On  exposed  surfaces  the  folds 
of  the  higher  orders  in  the  jaspilites  appear  as  a  series  of  crinklings  or 
flutings,  with  heights  of  from  one-quarter  inch  to  5  or  6  inches  from  trough 


U.   S.   GEOLOGICAL  SURVEY 


MONOGRAPH   XLVI       PL.    XX 


fs) 


8  inches 


FOLDS    IN    JASPILITES   OF   THE   VULCAN    FORMATION. 
A,  Pitching  fold  in  jaspilite  ;   /?,  lenses  of  jasper  inclosed  by  layers  of  schistose  hematite. 


ALGONKIAN,  VULCAN  FORMATION. 


357 


to  crest  (PI.  XX,  A).  In  some  cases  the  cross  sections  of  these  have  smooth 
and  flowing  contom's  with  rounded  turns,  and  in  other  cases  they  have 
straight  hmbs  witli  sharp,  angular  turns,  their  shapes  depending  largely 
upon  the  shapes  of  the  lai-ger  folds  upon  which  the  smaller  ones  are  super- 
posed. In  some  places  the  folds  are  open  and  at  other  places  they  are 
greatly  compressed.  In  the  sharper  folds  the  rock  in  the  turns,  i.  e.,  at  the 
axes  of  the  crests  and  the  troughs,  is  often  crushed  to  a  breccia,  the  frag- 
ments being  cemented  together  by  deposits  of  dolomite  or  siderite  or  of  ore. 
In  other  cases  the  siliceous  bands  at  the  turns  are  replaced  by  ore  into 
which  the  jasper  passes  gradually  both  vertically  and  transversely. 

While  the  folds  of  the  high  orders  are  most  noticeable  within  the  troughs 
of  the  dolomite  folds,  they  are  by  no  means  limited  to  these  situations. 
Many  minor  folds  are  found 
also  in  those  portions  of  the 
formation  where  there  are  no 
visible  folds  of  larger  dimen- 
sions, and  even  in  compara- 
tively small  specimens  of  jaspi- 
lites  there  may  be  gently  folded 
layers  included  between  con- 
siderable thicknesses  of  other 
layers  in  which  there  is  no 
evidence  of  contortions  of  any 
kind.  In  nearly  all  instances 
the  folded  layers  are  more 
richly- ferruginous  than  the  uncontorted  ones,  and  in  some  instances  they 
have  been  changed  completely  to  ore,  while  the  straight  layers  are  practi- 
cally pure  jaspers. 

Much  of  the  thickness  of  the  iron  formation  in  some  portions  of  the 
district  is  due  to  the  repeated  recurrence  of  the  same  layers  in  consequence 
of  the  minor  folding.  The  east  side  of  the  old  Keel  Ridge  pit  in  sec.  32, 
T.  40  N.,  R.  30  W.,  exhibits  this  effect  in  a  fine  manner.  The  pit  has  been 
abandoned  for  some  time  and  its  walls  are  partly  covered  by  fallen  matei'ial, 
but  enough  of  the  surface  can  be  seen  to  show  the  presence  of  folds  of  two 
orders  (see  fig.  24).  Folds  of  tertiary  and  higher  orders  are  well  seen  also 
on   the  stripped  surface  of  the   Traders  jaspilites  at  the  west  end  of  the 


.  24.— Diagrammatic  sketch  illustrating  folding  in  the  iron  forma- 
tion on  east  side  of  pit  at  old  Keel  Ridge  mine.  Area  about  20 
feet  by  20  feet. 


358 


THE  :menominep:  ikon-bearing  district. 


Clifford  pit  of  the  Traders  mine  (see  fig'.  25),  and  those  of  the  third  order  can 
again  be  seen  on  the  wall  of  the  pit  immediately  under  the  plan  shown 
in  fig.  25  (see  also  PI.  XVII,  B).     The  Brier  slates,  as  would  be  expected, 

were  much  more  subject  to  minor  folding  than 
the  two  more  rigid  sei'ies  of  jaspilites  between 
which  the  slates  are  included.  Small  folds  and 
crinkles  are  therefore  much  more  frequentl}^ 
noticed  in  the  slate  member  than  in  the  iron- 
liearing  members.  Indeed,  there  is  scarcely  a 
single  slate  exposure  of  large  size  that  does  not 
exhibit  distortions  of  some  magnitude.  Some- 
times the  distortion  takes  the  form  of  a  slight 
change  from  the  normal  in  the  dip  of  the  slate  beds,  indicating  the  presence 
of  a  very  open,  gentle  fold ;  frequently  it  takes  the  form  of  a  sudden  mono- 
clinal  bend  in  the  bedding,  and  many  times  it  appears  as  a  series  of  crinkles. 


Scale 


2  fee; 


Fig.  25, — Sketch  illustrating  puckering 
in  jaspilite  on  stripped  surface,  west 
end  of  Clifford  pit.  Traders  mine,  1899. 


100  feet 


Fig.  26.— Sketch  illustrating  folding  in  Brier  slates,  on  wall  of  trench  from  No.  2  pit  extending  south.  West  Vulcan  mine. 

flutings,  or  puckerings  in  the  strata  without  affecting  their  dip  as  a  whole. 
The  g-eneral  character  of  the  minor  folding  of  the  slates  is  well  shown  on 
the  east  side  of  the  trench  extending  south  from  the  large  pit  near  the 
center  of  the  southeast  quarter  of  the  northeast 
quarter  of  sec.  9,  T.  39  N.,  R.  29  W.,  just  west  of 
No.  4  shaft  of  the  West  Vulcan  mine  (see  fig.  26), 
and  again  on  the  west  side  of  the  excavation  at 
the  Curry  shaft  No.  1  (fig.  27). 

SECONDARY   STRUCTCTKES   RESULTING    FROM    FOLDING. 


Fig.  27.— Sketch  illustrating  puckering 
in  Brier  slates,  west  side  of  cut  at 
Currv  shaft  Ko.  1. 


Wherever  folding  is  observed  within  the 
iron-bearing  formation,  it  is  noticeable  that  it  is 
best  preserved  in  the  siliceous  bands.  The  iron- 
ore  layers  between  the  siliceous  layers,  while  yielding  to  the  stresses  that 
produced  the  folding,  were  mashed  and  sheared  and  became  schistose. 
Where  the  compressing  forces  were  very  powerful,  a  slaty  cleavage  devel- 


ALGOiNK IAN,  VULCAN  FORMATION.  359 

oped  in  both  the  iron  ore  and  the  siUceous  layers,  as  may  well  be  seen  on 
the  surfaces  forming  the  west  side  of  the  Traders  open  pit.  In  the  siliceous 
layers  this  is  the  only  secondary  structure  observed,  while  in  the  ores  there 
is  present  in  addition  a  schistose  structure  nearly  parallel  to  the  bedding 
plane,  unless  this  has  been  obliterated  by  the  deposition  of  new  ore 
material.  Frequently,  however,  the  conditions  were  not  favorable  to  the 
production  of  cleavage  in  the  brittle  jaspers,  while  eminently  favorable  to 
the  production  of  schistosity  in  the  ores.  The  jasper  layers  are  then  folded 
into  sharp  folds.  They  are  thick  and  thin  alternately,  and  in  some  places 
are  broken  across  at  intervals,  making  a  breccia  of  jasper  fragments  in  a 
schistose  ore  matrix  (fig.  23).  The  banding  in  the  resulting  breccias  may 
be  either  in  the  direction  of  the  bedding,  when  the  detached  fragments  have 
not  been  moved  far  from  their  original  positions,  or  it  niay  be  in  a  direction 
transverse  to  the  bedding  when  they  have  been  moved  appreciable  amounts; 
for  in  the  latter  case  they  have  been  rotated  into  the  plane  of  the  motion 
and  taken  positions  corresponding  to  that  of  the  cleavage  in  the  ores.  The 
rocks  of  the  Traders  and  Clifford  pits  are  principally  breccias  of  this 
character.  Because  of  the  rounding  of  the  edges  of  the  jasper  fragments, 
the  rocks  look  very  much  like  conglomerates  (see  plan  of  Clifford  pit  for 
relations  between  folding  and  schistosity  at  this  place,  PI.  XXIV,  and 
p.  407,  for  descriptions  of  the  brecciated  rocks). 

THICKNESS. 

A  number  of  sections  offer  opportunities  for  determining  the  thickness 
of  the  separate  members  of.  the  Vulcan  formation,  but  only  a  few  present 
opjjortunities  foi'  determining  its  total  thickness. 

All  along  the  south  side  of  the  southern  dolomite  belt,  from  the  Aragon 
mine  eastward  to  the  Sturgeon  River,  the  iron-bearing  formation  stretches 
as  a  narrow  belt,  which  for  much  of  the  distance  appears  to  be  without 
important  folds.  At  several  places  mining  operations  have  afforded  excel- 
lent sections  from  the  base  of  the  productive  portion  of  the  Traders  member 
to  the  top  of  the  Curry  member,  and  at  a  few  places  the  sections  extend 
downward  to  the  top  of  the  Randville  dolomite.  At  Brier  Hill,  Avhere 
practically  the  whole  formation  can  be  seen  on  the  surface,  its  thickness  is 
about  600  feet.  At  the  Curry  shaft  No.  2  it  is  700  feet  thick,  and  at  the 
Aragon  mine  its  thickness  is  about  675  feet. 


360  THE   MENOMINEE  IKON-BEARING  DISTRICT. 

The  thickness  of  the  individual  members  comprising  the  fonnation  is 
easily  estimated  at  a  number  of  places.  The  Brier  slates  have  been  meas- 
ured at  seven  places,  yielding  results  between  100  and  360  feet.  Five  of 
these  measurements  fall  between  320  and  360  feet.  Eight  measurements 
of  the  Curry  member  have  given  results  varying  between  100  and  225  feet. 
Six  of  these  fall  between  160  and  225  feet.  Measurements  of  the  Traders 
member  have  not  yielded  such  concordant  results.  In  the  first  place,  its 
thickness  probably  varies  widely,  as  should  be  expected  of  a  formation 
composed  largely  of  detrital  deposits  laid  down  near  a  shore  line.  More- 
over, only  a  few  sections  reach  as  low  as  the  dolomite;  consequently  the 
exact  position  of  the  contact  between  this  rock  and  the  iron-bearing  for- 
mation must  be  guessed  at.  Only  three  measurements  have  been  made 
from  the  known  top  of  the  dolomite  to  the  known  top  of  the  Traders 
member.     These  give  170  feet,  85  feet,  and  155  feet. 

Favorable  opportunities  for  accurate  determinations  of  the  thickness 
of  the  Vulcan  formation  in  the  southern  iron-bearing  belt  west  of  Norway 
and  in  the  central  iron-bearing  belt  north  of  Lake  Antoine  are  very  poor. 
In  both  of  these  areas  folding  is  more  prominent  than  it  is  in  the  southern 
belt  east  of  Norway,  and  where  folding  is  not  prominent  exposures  are 
lacking.  In  the  Pewabic  mine  a  measured  section  along  a  drift  in  the  first 
level  under  shaft  No.  1  gave  232  feet  for  the  Traders  member  and  265  feet 
for  the  Brier  slates.  Near  the  center  of  sec.  6,  T.  39  N.,  R.  29  W.,  the 
measured  width  of  the  Curry  member  is  350  feet.  The  dip  of  the  jaspilites 
is  not  known,  but  it  is  about  75°.  The  thickness  calculated  on  this  dip  is 
over  325  feet.  At  the  Traders  mine  195  feet  of  the  Traders  member  are 
exposed,  but  because  of  close  folding  and  lack  of  exposures  no  estimate  of 
the  thickness  of  the  remaining  members  of  the  formation  is  hazarded.  At 
the  Indiana  mine  the  measured  thickness  of  the  entire  Vulcan  formation  is 
about  550  feet.  At  the  Forest  mine,  in  sec.  25,  T.  39  N.,  R.  29  W.,  a  drill 
hole  penetrated  about  130  feet  of  the  Traders  member. 

An  interesting  feature  of  these  figures  appears  when  we  compare  the 
estimated  thickness  of  the  Brier  and  the  Curry  members  with  the  total 
thickness  of  the  two.  In  almost  every  case  where  the  estimated  thickness 
of  either  of  these  members  falls  below  the  average  of  all  the  measure- 
ments for  that  member  the  thickness  of  the  other  member  exceeds  the 
average,  and  the  total  of  the  two  is  fairly  constant.     Thus,  whereas  seven 


ALGONKIAN,  VULCAN  FORMATION.,  361 

estimates  of  the  thickness  of  the  Brier  slates  vary  between  240  feet  and 
360  feet,  and  nine  estimates  for  the  Curry  member  vary  between  112  feet 
and  325  feet,  measurements  of  the  total  thickness  of  the  two  vary  only 
between  400  and  630  feet.  The  apparent  greater  variation  in  thickness 
of  each  of  the  members  than  the  two  combined  may  be  partly  explained 
as  due  to  the  gradation  between  them  and  the  consequent  difficulty  of 
fixing  upon  the  exact  place  at  which  one  ends  and  the  other  begins. 

From  a  careful  consideration  of  the  figures  given  above  and  a  few 
others  that  are  not  here  recorded  it  is  estimated  that  the  average  thick- 
ness of  the  Vulcan  formation  is  approximately  650  feet,  divided  as  fol- 
lows: Traders  member,  where  it  is  fully  developed,  150  feet;  Brier  slates, 
330  feet;  Curry  member,  170  feet — i.  e.,  the  two  ore-bearing  members 
combined  about  equal  in  thickness  the  intervening  slates.  Of  course  it  is 
understood  that  by  overlapping,  one,  two  or  all  the  members  of  the  forma- 
tion may  disappear  from  the  surface,  though  they  may  exist  with  their 
full  thicknesses  at  some  little  depth  beneath  it. 

RELATIONS  BETWEEN  THE  VULCAN  AND  ADJACENT  FORMATIONS. 

The  relations  between  the  Vulcan  formation  and  the  underlying 
dolomite  have  been  repeatedly  discussed  in  the  preceding  pages.  It 
seems  unnecessary  to  repeat  the  statements  already  made  concerning  these 
relations.  Under  the  present  head  the  facts  discovered  that  throw  light 
on  them,  and  the  conclusions  to  which  these  facts  lead,  are  summarized, 
and  a  few  additional  facts  are  described  which  explain  the  absence  of  the 
iron  formation  from  some  portions  of  the  district  where  it  would  naturally 
be  expected  to  occui-. 

The  iron-bearing  Vulcan  formation,  except  in  very  limited  areas,  is 
known  to  rest  upon  the  Randville  dolomite.  Where  they  can  be  seen  the 
lower  layers  of  the  upper  formation  appear  to  lie  conformably  u^^on  the 
older  one,  usually  with  an  extremely  sharp  line  of  definition  between  them. 
In  some  places  the  upper  part  of  the  Randville  formation  is  a  dolomite.  In 
other  places  it  is  a  talcose  schist  derived  from  the  dolomite.  Where  the 
Vulcan  formation  rests  on  the  dolomite  or  talcose  schist  its  basal  member  is 
either  a  thin  bed  or  series  of  beds  of  slate,  a  quartzite  which  often  contains 
ore  and  jaspilite  fragments,  or  an  ore  and  jasper  conglomerate  containing 
large  and  small  pebbles  of  ore.     In  some  cases  the  slate  is  absent,  but  in 


362  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

every  case  the  quartzite  or  conglomerate  is  present  either  at  or  very  near 
the  base  of  the  formation.  The  fragments  in  the  conglomerates  must  have 
been  derived  from  an  older  iron  formation  that  originally  rested  upon  the 
dolomite,  but  which  was  eroded  at  the  time  the  Traders  member  was  laid 
down.  In  one  case,  at  least,  the  dolomite  itself  yielded  bowlders  to  the 
overlying  beds,  for  on  the  seventh  and  eighth  levels  of  the  Chapin  mine,  at 
a  point  just  south  of  shaft  "C,"  several  large  rounded  fragments  of  the  dol- 
omite were  found  embedded  in  the  iron-bearing  formation.  If  there  was 
originally  a  slight  discordance  in  bedding  between  the  two  formations,  it  has 
been  obliterated  by  the  movements  along  the  contact  plane  that  took  place 
during  the  folding  of  the  district.  The  Traders  member  thus  appears  to 
be  conformable  in  attitude  with  the  underlying  dolomite,  which  remained 
practically  undisturbed  during  the  long  interval  which  succeeded  its 
deposition  and  preceded  the  deposition  of  the  Traders  member. 

Along  the  north  side  of  the  Norway  syncline  and  in  the  belt  north  of 
the  Curry  and  the  West  Vulcan  mines  in  sec.  9,  T.  39  N.,  R.  29  W.,  the 
movements  along  the  contact  plane  were  so  vigorous  that  they  caused 
brecciation  in  the  rocks  on  both  sides  of  it.  On  the  dolomite  side  of  the 
contact  the  rock  is  affected  by  the  brecciation  only  to  a  limited  depth.  For 
a  short  distance  beneath  its  upper  siirface  it  consists  of  a  mass  of  large  frag- 
ments and  bowlders  of  dense  dolomite  embedded  in  a  soft,  sheared  matrix 
composed  of  serpentine,  talc,  and  aii  earthy  substance  often  colored  slightly 
by  limonite.  On  the  upper  side  of  the  contact  the  brecciation  has  affected 
the  entire  Traders  member  and  a  portion  of  the  Brier  slates  (PI.  XXI,  A), 
causing  them  in  many  places  to  resemble  strongly  true  conglomerates 
The  resemblance  of  the  ore  breccia  is  so  sti'ikingly  like  that  of  the  Ishpem- 
ing  conglomerate  at  the  base  of  the  Upper  Marquette  series  that  at  first 
glance  it  was  taken  to  represent  a  basal  conglomerate  at  the  bottom  of  the 
Upper  Menominee  series.  It  contains  large  bowlder-like  masses  of  ore  and 
jasper  in  a  schistose,  or  specular,  ore  matrix  (see  PI.  XXII,  A)  exactly  like 
the  conglomerate  above  the  Negaunee  formation  in  the  Marquette  district. 
When  traced  upward,  however,  the  rock  in  some  places  is  seen  to  pass  into 
a  slate  breccia  in  which  the  matrix  is  a  serpentinized  slate  and  the  bowl- 
ders or  fragments,  either  slate  or  ore,  or  an  intermingling  of  both.  In 
the  Norway  sjTicline  the  brecciation  extends  far  upward  into  the  Brier 
slates,   in  some  places   crushing  them   throughout  their  entire  thickness. 


PLATE   XXI. 


363 


PLATE    XXI. 

Fig.  ^-1. — Brecciated  Bkier  slates.  In  Norway  pit,  near  the  contact  of  the  slates  with  the 
underlying  ores  of  the  Traders  member. 

The  surface  photographed  was  a  portion  of  a  wall  bounding  a  mass  of  the  slate  near  the  center 
of  the  pit.  This  mass  was  left  in  the  pit  because  it  was  not  quite  rich  enough  in  iron  to  warrant 
mining.     Other  portions  of  this  same  breccia  had  been  mined  and  shipped  as  lean  ore  (1899). 

Fig.  B. — Band  of  brecciated  Brier  slate  crossing  definitely  bedded  slates  transversely 
TO  their  bedding.     In  Norway  pit. 

The  bedding  of  the  unbrecciated  slate  is  from  right  to  left.  The  breccia  band  truncates  the 
layers.  In  this  breccia  the  fragments  and  matrix  originally  had  the  same  composition,  but  the  finely 
comminuted  texture  of  the  latter  afforded  favorable  conditions  for  the  deposition  in  it  of  ferruginous 
and  taleose  materials.  Consequently  the  matrix  is  now  softer  than  the  fragments,  and  hence  is  more 
easily  eroded,  and  at  the  same  time  it  is  more  highly  ferruginous. 

364 


U.   S.   GEOLOGICAL   SURVEY 


MONOGRAPH    XLVI       PL.    XXI 


A.      BRECCIATED    BRIER   SLATES    IN    NORWAY    PIT. 


B.     BAND   OF    BRECCIATED    BRIER   SLATE   CROSSING    DEFINITELY    BEDDED   SLATES   TRANSVERSELY   TO   THEIR 

BEDDING,    IN    NORWAY    PIT. 


ALGONKIAN,  VULCAN  FORMATION.  365 

The  fragments  are  nearly  all  sharp  edged  (see  PI.  XXI,  A).  If  there  were 
any  doubt  as  to  the  true  character  of  the  rock,  the  existence  of  brecciated 
bands  crossing  the  rock  transversely  to  its  bedding  would  effectually 
remove  it  (see  PI.  XXI,  J5).  The  lack  of  sharp  contacts  in  this  area 
between  the  dolomite  and  the  members  of  the  iron  formation  aiid  the 
complexity  of  their  mutual  relations  is  thus  plainly  due  to  brecciation  of 
the  beds  bordering  the  contact  planes,  and  not  to  any  confusion  in  their 
stratigraphical  positions.  Here,'  as  elsewhere,  the  Vulcan  formation  was 
deposited  upon  the  Randville  dolomite  and  was  followed  conformably  by 
the  Brier  slates.  Movement  in  a  zone  near  the  contact  plane  crushed  the 
rocks  and  produced  brecciation  and  schistosity.  The  motion  must  have 
taken  place  sometime  after  the  deposition  of  the  Brier  slates,  but  before 
the  deposition  of  the  Lake  Superior  sandstone  which  overlies  the  breccias 
in  horizontal  layers.     It  was  probably  contemporaneous  with  the  folding. 

The  relations  between  the  Vulcan  formation  and  the  overlying  Han- 
bury  slates  are  also  those  of  conformity.  The  contact  is  usually  very 
sharp.  Little  difficulty  is  experienced  in  defining  the  upper  limit  of  the 
iron-bearing  formation  where  exposures  are  plentiful.  The  slates,  however, 
are  often  so  very  schistose  on  the  upper  side  of  the  contact  that  their  bed- 
ding planes  can  not  be  recognized.  In  most  places  the  overlying  slates  are 
strongly  graphitic  and  often  very  fissile.  Where  not  graphitic  they  are 
light  silvery  schists  from  which  all  bedding  traces  have  disappeared.  The 
bedding  of  the  iron-bearing  formation,  on  the  other  hand,  is  still  almost 
perfectly  preserved,  and  is  parallel  to  the  contact.  In  one  or  two  places 
the  iron-bearing  beds  are  separated  from  the  slates  by  narrow  bands  of  a 
soft  earthy  green  rock  containing  remnants  of  plagioclase  and  a  mass  of 
green  chloritic  products  such  as  visually  result  from  the  decomposition  of  a 
basic  eruptive.  The  green  rock  has  the  appearance  of  a  dike,  which  it 
probably  is,  that  intruded  the  bedded  series  along  the  contact  plane. 
Dikes  of  this  kind  are  common  in  the  Hanbury  slate  area,  but  are  rarely 
seen  in  the  Vulcan  formation.  The  best  preserved  example  of  one  of  these 
contact  dikes  is  that  on  the  east  wall  of  the  large  pit  at  shaft  No.  1  of  the 
West  Vulcan  mine.  Here  the  dike,  as  far  as  it  can  be  traced,  follows 
the  contact  between  the  Curry  jaspilites  and  the  gray  schistose  slates  of 
the  Hanbury  formation. 

At  a  few  other  places,  as,  for  instance,  in  the  neighborhood  of  the 


366  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Pewabic  mine,  faults  may  intervene  between  the  iron-bearing  formation 
and  the  overlying  slate.  They  are  apparently  of  little  importance  from 
a  structural  point  of  view,  but  have  not  yet  been  sufficiently  exposed  to 
warrant  any  very  definite  statements  as  to  their  extent  or  position  with 
reference  to  the  adjacent  rocks.  The  fault  in  the  Pewabic  mine  separates 
the  Traders  quartzite  from  the  Brier  slate  where  it  is  best  exposed,  but  it 
probably  extends  to  the  west,  where  it  must  pass  between  the  Cuny  and 
the  Haubury  beds  unless  it  terminates  suddenly  (see  map,  PI.  XXVIII 
and  fig.  35). 

The  relations  between  the  Hanbury  slate  and  the  formations  older  than 
the  Vulcan  formation  should  perhaps  logically  be  considered  under  the 
Hanbury  slate  rather  than  in  this  place.  However,  these  relations  are 
so  connected  with  the  relations  of  the  Vulcan  formation  that  the  subject  is 
here  introduced.  A  further  reason  for  this  treatment  is  that  the  relations 
of  the  Hanbury  slate  have  an  important  bearing  upon  the  possible  distribu- 
tion of  the  beds  of  the  Vulcan  formation,  which  carry  the  iron  ores. 

At  only  one  point  has  the  actual  contact  between  the  Randville  dolo- 
mite and  Hanbury  slate  been  seen.  This  is  in  a  trench  about  10  feet  long 
in  graphite-slates  near  the  east  line  of  sec.  2,  T.  39  N.,  R.  30  W.,  a  few  rods 
west  of  the  Bryngelson  shaft.  A  careful  examination  of  the  relations 
between  the  dolomite  and  slate  was  made,  with  special  reference  to  their 
bearing  upon  unconformity  and  faulting  It  was  found  that  the  dolomite 
projects  slightly  into  the  slates  halfway  up  the  exposed  portion  of  the  con- 
tact, and  recedes  from  them  both  above  and  below  this  point.  The  surface 
of  the  dolomite  is  minutely  irregular,  small  projections  and  reentrants 
occurring  throughout  the  entire  line  of  contact.  The  slates,  which  are 
strongly  graphitic,  are  interlaminated  with  cherty  bands.  They  contain 
small  fragments  of  the  dolomite  and  are  badly  shattered.  A  slate  breccia 
is  thus  formed,  which  might  be  a  fault  breccia  or  a  brecciated  conglomerate. 
There  can  be  no  doubt  that  there  has  been  movement  along  the  contact 
zone,  for  the  bedding  of  the  slate  has  been  much  disturbed  for  a  distance  of 
8  feet  or  moi'e  from  the  dolomite.  Whether  or  not  the  movement  was  along 
a  fault  plane  which  cut  out  the  Vulcan  formation  was  not  determinable 
from  the  exposures.  The  dolomite  along  the  contact  plane  is  not  slicken- 
sided,  nor  is  the  rock  near  the  contact  greatly  mashed,  so  far  as  could  be 
observed.     This  may  be  thought  to  indicate  that  the  movement  was  of  slight 


PLATE  XXII. 


367 


PLATE   XXII. 

Fig.  a. — Surface  of  ore  breccia.  Near  contact  of  the  Traders  member  with  overlying  Brier 
slate,  No.  3  pit,  Curry  mine,  southwest  quarter  of  northeast  quarter,  sec.  9,  T.  39  N.,  E.  29  W. 

The  brecciated  rock  was  a  banded  jaspilite.  The  surface  shown  is  the  surface  of  a  band  of 
specular  hematite.  The  large  lenticular  fragments  of  jasper  embedded  in  the  schistose  ore  matrix 
make  their  presence  known  by  causing  projections  and  depressions  in  its  surface.  To  the  right,  in  the 
liackground,  distinctly  bedded,  unbrecciated  jaspilites  can  be  seen. 

Fig.  B. — CoNCEXTRATiNG  WORKS  AT  THE  Pewabic  PIT.     Photograph  by  J.  J.  Eskil. 

The  rough  ore  used  is  the  conglomerate  at  the  base  of  the  Lake  Superior  sandstone.  This  is 
crushed,  and  the  hematite  is  separated  from  the  sand  by  washing. 

To  the  left  of  the  building  is  a  cliff  of  cherty  dolomite. 

368 


U.    S.    GEOLOGICAL    SURVEY 


MONOGRAPH    XLVI       PL.    XXII 


A.     SURFACE  OF   ORE   BRECCIA   NEAR   CONTACT  OF   THE  TRADERS    MEMBER   WITH    THE    BRIER   SLATES, 

NO.   3    PIT.   CURRY    MINE, 


J!      CONCENTRATING   WORKS   AT    PEWABIC    PIT. 


ALGONKIAN,  VULCAN  FORMATION.  369 

magnitude,  and  that  it  was  more  in  the  nature  of  a  differential  movement  of 
the  slates  near  the  contact  than  of  faulting  across  the  beds.  If  the  absence 
of  the  iron-bearing  beds  between  the  Hanbuiy  slate  and  the  dolomite  is 
due  to  overlapping  of  the  slates  rather  than  to  faulting,  the  lower  layers  of 
the  slate  should  be  coarse  detritus,  since  the  relation  of  the  slates  to  the 
underlying  rocks  are  those  of  a  younger  sedimentary  series  to  an  older 
series  upon  which  the  younger  series  is  unconformable.  The  breccia 
between  the  slate  and  the  dolomite  referred  to  above  may  be  a  mashed 
conglomerate  of  this  kind. 

At  Iron  Hill,  in  sec.  32,  T.  40  N.,  R.  29  W.,  the  Hanbury  slate  is 
believed  to  lie  immediately  upon  the  Randville  dolomite,  although  no  con- 
tact between  the  two  is  seen  (see  PI.  XLII).  The  dolomite  ends  in  a 
number  of  small  knobs  having  steep  faces  toward  the  south.  At  the  bases 
of  the  little  cliffs  is  a  swamp  about  300  feet  wide,  and  upon  the  opposite 
side  of  the  swamp,  on  the  north  slope  of  a  slight  elevation,  are  several 
exposures  of  slate.  The  intervening  swamp  area  has  been  tested  at  a  num- 
ber of  places  by  auger  borings,  as  has  already  been  related,  and  has  been 
found  to  be  underlain  by  slates. 

The  uppermost  layers  of  the  dolomite  formation  consist  of  white  cherts, 
and  these  are  beautifully  brecciated.  Below  these  in  some  places  lies  a 
conglomerate  containing  numerous  large  rounded  bowlders  of  dolomite, 
subangular  fragments  of  chert,  and  an  occasional  pebble  of  quartzite  in  a 
matrix  composed  mainly  of  dolomite  and  chert  d(ibris  (see  PI.  XVI,  B). 
Many  of  the  pebbles  are  mashed  and  faulted,  showing  that  the  district  was 
deformed  after  the  conglomerate  was  laid  down.  When  the  conglomerate 
is  traced  eastward  to  the  end  of  the  set  of  dolomite  ledges,  the  relations 
between  this  rock  and  the  chert  are  found  to  be  very  complicated.  The 
conglomerate  apparently  grades  into  a  breccia,  and  this  in  places  is  between 
beds  of  dolomite  or  layers  of  the  chert.  At  one  place  the  conglomerate 
looks  as  though  it  were  a  breccia  formed  by  crushing  of  the  chert  and 
dolomite;  at  other  places  it  appears  to  be  a  layer  of  true  conglomerate 
between  layers  of  massive  dolomite,  and  in  other  places  it  strongly  resem- 
bles a  conglomerate  composed  of  fragments  of  the  dolomite  and  chert 
lying  above  the  dolomite.  The  conglomerate  may  be  an  intraformational 
conglomerate  (one  originally  produced  during  the  deposition  of  the  forma- 
tion, and  therefore  an  integral  part  of  it),  whose  complex  relations  to  the 

MON  XLVI — 04 24 


370  THE   MENOMINEE  IKON-BEARING  DISTRICT. 

remainder  of  the  Randville  dolomite  are  due  to  crushing  and  close  folding; 
or,  on  the  other  hand,  it  may  be  a  true  conglomerate  at  the  base  of  the 
Hanbmy  slate,  made  to  appear  like  an  intraformational  conglomerate  by- 
repeated  close  folding  at  the  end  of  an  eastward-pitching  anticline  on  which 
are  superposed  several  minor  folds.  The  latter  is  thought  to  be  the  proba- 
ble explanation.  If  this  be  correct,  the  difference  in  composition  of  the 
conglomerate  from  the  normal  slates  is  explained  by  its  being  the  first 
deposit  along  a  shore  line  composed  of  dolomites  and  cherts.  But  the 
relations  of  the  various  rocks  at  this  place  are  so  exceedingly  complicated 
that  no  unprejudiced  observer  would  be  willing  to  declare  without  reserva- 
tion that  the  conglomerate  is  not  a  member  of  the  dolomite  formation, 
rather  than  the  basal  member  of  the  Hanbury  slate  (see  also  pp.  256  and 
481  for  fuller  descriptions  of  the  relations  at  this  place). 

EXPLANATION  OF  THE  DISTRIBUTION  AND  RELATIONS  OF  THE  VULCAN  AND 
HANBURY  FORMATIONS  TO  THE  UNDERLYING  FORMATIONS. 

Two  possible  explanations  suggest  themselves  to  account  for  the  facts 
of  distribution  of  the  Vulcan  and  Hanbury  formations,  their  relations  to 
the  adjacent  formations,  and  the  character  of  their  basal  members,  faulting 
and  uiiconformity. 

For  a  time  it  was  thought  that  faulting  near  the  contact  plane 
between  the  Hanbury  slate  and  the  older  rocks  might  explain  the  phenom- 
ena. Thus  the  absence  of  the  Vulcan  formation  east  of  Quinnesec  could 
be  explained  by  the  hypothesis  that  the  Hanbury  slates  had  been  thrust 
over  the  lower  formation  of  the  Upper  Menominee  series  so  as  to  rest  upon 
the  Randville  dolomite.  The  absence  of  the  Vulcan  formation  between 
the  Hanbury  slate  and  the  dolomite  at  Iron  Hill  might  similarly  be 
explained,  only  here  it  would  be  necessary  to  believe  that  after  the  faulting 
occurred  close  folding  took  place,  else  the  manner  in  which  the  Hanbury 
slate  wraps  around  the  eastern  end  of  the  central  belt  of  dolomite  would 
be  inexplicable. 

There  are  undoubted  minor  faults  in  the  Menominee  district,  but  most 
of  them  are  extremely  small,  those  in  the  Pewabic  mine  being  the  only 
ones  of  sufficient  magnitude  to  be  mapped  on  the  mine  plat.  Moreover,  it 
is  clear  that  the  crushed  zones  of  the  Traders  and  Brier  beds  at  the  Nor- 
way, Curry,  and  West  Vulcan  locations  are  due  to  faulting.     Further,  there 


ALGONKIAN,  VULCAN  FORMATION.  371 

have  been  marked  movements  of  accommodation  between  the  different 
formations  at  theii*  contacts,  which  might  be  called  faulting.  In  all  of  these 
instances,  however,  the  faidts  are  local,  and  in  none  of  them  is  the  displace- 
ment of  the  faulted  beds  great.  These  few  minor  faults,  which  are  easilv 
recognized,  certainly  would  not  warrant  the  assumption  of  such  numerous 
and  extraordinary  faults  as  would  be  necessary  to  explain  the  relations 
above  described.  Furthermore,  the  faulting  theory  does  not  explain  the 
conglomeratic  and  quartzitic  character  of  the  Vulcan  formation  where  it  is 
in  contact  with  the  Randville  dolomite,  nor  does  it  explain  the  apparent 
conglomerates  found  at  several  places  at  the  base  of  the  Haubury  slate. 

The  second  explanation  which  suggested  itself  is  founded  on  the  belief 
that  an  unconformity  exists  between  the  Lower  Menominee  and  the  Upper 
Menominee,  such  as  exists  elsewhere  between  the  Upper  Huronian  and  the 
Lower  Huronian  in  the  Lake  Superior  region.  The  order  of  events  pro- 
ducing the  .unconformity  must  have  been  somewhat  as  follows:  After  the 
deposition  of  the  Lower  Huronian  series,  consisting  of  the  Sturgeon  quartz- 
ite,  the  Randville  dolomite,  and  the  iron-bearing  Negaunee  formation,  the 
area  was  raised  above  the  sea.  Denudation  continued  for  a  long  time.  Upon 
the  southern  side  of  the  Menominee  trough  these  formations,  if  deposited, 
were  entirely  removed.  In  the  central  and  northern  portions  of  the  district 
denudation  extended  to  a  sufficient  depth  to  remove  the  Negaunee  forma- 
tion in  the  larger  part,  if  not  all,  of  the  area,  and  to  cut  into  the  Randville 
dolomite.  Probably  the  folding  accompanying  this  uplift  and  erosion  was 
very  moderate.  After  erosion  had  long  continued,  there  was  slow  subsidence 
of  the  Lower  Menominee  land.  During  the  early  stages  of  the  encroach- 
ment of  the  sea  ujwn  the  land  the  Vulcan  formation  was  laid  down.  As 
shown  by  the  character  of  this  formation,  it  consists  largely  of  detrital 
ore-formation  material.  This  was  derived  from  the  Lower  Menominee 
Negaunee  formation,  which  during  the  course  of  the  erosion  had  practically 
all  disappeared.  However,  at  the  end  of  Vulcan  time  the  sea  had  not  yet 
wholly  overridden  the  land,  for  at  some  places  certainly,  and  perhaps  for 
extensive  areas,  the  Vulcan  formation  is  not  present.  After  Vulcan  time 
the  subsidence  of  the  land  continued  during  the  deposition  of  the  Haubury 
slate.  In  places  where  the  Lower  Menominee  series  was  below  the  sea  at 
the  beginning  of  Vulcan  time  the  Haubury  slate  rests  upon  the  Vulcan 
formation.     Where  the  Lower  Menominee  series  was  above  the  sea  at  the 


372  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

beginning  of  Vulcan  time,  but  was  depressed  beneath  the  sea  at  the  end  of 
this  period,  the  slate  overlapped  the  underlying  Vulcan  rocks  and  now  rests 
directly  upon  the  Lower  Menominee  series,  as,  for  instance,  at  Iron  Hill 
and  at  the  locality  east  of  Quinnesec  to  which  reference  has  been  made. 

The  theory  of  unconformity  with  overlap  thus  fully  and  satisfactorily 
explains  every  fact  of  distribution  and  every  known  relation  between  the 
Upper  Menominee,  the  Lower  Menominee,  and  the  Archean  rocks.  The 
presence  of  a  great  quantity  of  detrital  ores,  of  quartzites,  and  of  ore  and 
iasper  conglomerates  near  the  base  of  the  Vulcan  formation  is  fully 
explained.  The  absence  of  tlie  Vulcan  formation  from  various  parts  of  the 
district  also  presents  no  difficulty,  these  being  areas  which  were  still  above 
the  sea  during  Vulcan  time.  The  disappearance  of  the  Traders  member 
first  among  the  Vulcan  beds  and  its  absence  from  strips  of  country  in  which 
the  Curry  member  is  to  be  found,  and  the  gradual  approach  of  the  base  of 
the  Hanbury  slates  to  the  Lower  Huronian  at  such  places  are  likewise 
made  clear. 

It  is  therefore  with  great  confidence  that  the  second  theory  is  proposed 
to  explain  the  structural  phenomena  of  the  district — the  theory  of  uncon- 
formity between  the  Lower  Menominee  and  the  Upper  Menominee  series, 
with  a  gradual  advance  of  the  Upper  Menominee  sea,  the  deposits  of  which 
slowly  overlapped  the  earlier  deposits  and  gradually  buried  the  higher 
lands  composed  of  the  Lower  Menominee  rocks. 

According  to  this  theory  there  are  in  the  Menominee  district  all  the 
evidences  of  a  great  unconformity  between  the  Upper  Menominee  and 
the  Lower  Menominee — an  unconformity  like  that  found  in  the  Huronian 
of  the  Marquette  district  and  other  districts  of  the  Lake  Superior  region, 
except  that  in  the  Menominee  district  there  is  no  marked  discordance  in 
strike  and  dip  between  the  upper  and  lower  series.  This  lack  of  discord- 
ance does  not  in  the  least  invalidate  the  conclusion  that  a  great  time  gap 
separates  the  two  series.  It  has  been  shown  by  Vaia  Hise,"  that  an  appar- 
ently minor  unconformity  ma)'  mark  as  great  a  time  interval  as  the  most 
startling  discordance.  The  relations  of  the  two  series  in  the  Menominee 
district  are  very  similar  to  those  existing  in  the  Penokee  district  between 
the  cherty  limestone  of  the  Lower  Hux'onian  and  the  Upper  Huronian 
quartz-slate  member. 

oVanHise,  C.  R.,  Principles  of  North  American  pre-Cambrian  Geology:  Sixteenth  Ann.  Rept. 
U.  S.  Geol.  Survey,  pt.  1,  1894. 


ALGONKIAN,  UPPER  MENOMIMEE  SERIES.  373 


THE  ORES. 

LITHOLOGY. 

PHYSICAL    CHARACTERS. 


The  ores  occiirring  in  the  Vulcan  beds  have  been  incidently  referred, 
to  repeatedly  in  the  preceding  laaragraphs,  and  the  characteristics  of  some 
phases  of  them  have  been  described.  Under  the  present  head  a  general 
description  of  the  ores  is  presented  and  a  few  statements  are  made 
concerning  their  composition,  without  respect  to  their  position  in  the  forma- 
tion. In  general,  the  Traders  and  the  Curry  ores  are  not  very  different, 
though  there  are  some  varieties  in  the  lower  member  that  have  not  yet  been 
discovered  in  the  upper  member,  and  there  are  others  that  are  peculiarly 
characteristic  of  the  U2:)per  member.  Under  the  term  ores  is  included  not 
only  the  material  now  being  shipped,  but  also  that  which,  in  the  near 
future,  must  be  drawn  upon  to  meet  the  demand  when  the  richer  supplies 
have  become  scarcer  or  exhausted.  The  character  of  the  ore  varies  from 
year  to  year  in  the  smaller  mines,  as  old  deposits  are  worked  out  and  new 
ones  are  exploited,  and  also,  to  some  degree,  in  accordance  with  the  condi- 
tion of  the  ore  market,  which  may  enable  ores  to  be  profitably  worked  in 
certain  seasons  which  in  other  seasons  would  not  begin  to  pay  the  cost  of 
mining. 

A  rough  division  of  the  ores  of  the  district  is  into  siliceous  ores  and  rich 
ores;  and  these  classes  may  be  subdivided  into  different  grades,  based 
partly  upon  their  chemical  and  partly  upon  their  physical  characters. 

The  siliceous  ores  are,  in  part,  simply  very  rich  portions  of  the  iron 
formation,  retaining  its  original  physical  characteristics,  and  in  part  portions 
of  the  formation  in  which  some  of  the  jasper  of  the  jaspilites  has  been 
replaced  by  ferruginous  material.  In  the  latter  class  the  physical  aspects 
of  the  jaspilites  have  suffered  great  modifications.  These  two  classes  of 
ores  pass  into  one  another  and  into  typical  jaspilites  too  poor  in  hematite  to 
warrant  mining  at  present,  and  the  second  class  grades  into  rich  ore,  from 
which  i^ractically  all  the  silica  has  been  extracted.  In  both  classes  the 
original  banding  of  the  jaspilites  is  often  preserved  with  great  perfection. 
This  banding  extends  without  disturbance  from  ore  to  jaspilite,  the  passao-e 
between  the  two  being  accomplished  both  by  lateral  and  by  vertical  grada- 
tions.    The  difference  between  the  two  classes  is  mainly  one  of  decree  of 


374  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

alteration.  The  ores  of  the  first  class  retain  more  nearly  their  original 
character  than  those  of  the  second  class.  The  former  are  but  slightly 
changed  phases  of  the  original  deposits,  to  which  some  hematite  has  been 
added  by  alteration  of  their  original  ferruginous  component,  while  the 
latter  are  largely  replacements  of  the  original  materials  through  the  removal 
of  quartz  by  solution  and  the  deposition  in  its  place  of  derived  hematite. 

In  those  cases  in  which  the  ores  consist  of  enriched  portions  of  the 
iron  formation  they  possess  the  general  aspects  of  the  ferruginous  bands  in 
the  original  jaspilites.  The  ores  may  be  even-banded  bluish-black  rocks 
composed  of  alternating  tliin  layers  of  hematite  and  of  very  feiTuginous 
jasper,  with  the  hematite  layers  greatly  in  excess,  or  they  may  consist  of 
thick  layers  of  hematite  separated  by  thin  layers  of  jasper.  Laminae  of 
dense  black  hematite  sometimes  run  through  the  deposits  parallel  to  their 
bedding,  emphasizing  this  structure  and  making  the  ore  very  hard.  Whevi 
(Occurring  in  sheared  portions  of  the  formation,  the  ores  are  more  or  less 
micaceous  and  specular,  as  at  the  Traders  mine,  but  none  of  the  ores  now 
mined  are  as  typically  specular  as  some  of  those  on  the  Marquette  range. 
'The  micaceous  varieties  are  limited  exclusively  to  the  lower  portion  of 
the  Traders  member,  and  are  thus  in  the  same  stratigraphical  ^^ositiou  as 
the  corresponding  ores  in  the  Marquette  district.  The  nonspecular  lean 
ores  have  in  general  a  rather  dull  luster  and  a  texture  that  is  dense  or 
granular,  according  to  the  proportion  of  the  dense,  flinty,  vein-like  hema- 
tite in  them  or  to  the  proportion  of  quartz  grains  intermingled  with  the 
ferruginous  material.  When  the  proportion  of  quartz  grains  is  large,  the 
ore  takes  on  a  gray  tinge  and  becomes  more  or  less  friable  or  sandy. 
When  the  ores  contain  but  little  quartz  and  no  vein-like  hematite,  they  are 
very  close  grained,  fairly  hard,  and  finely  granular,  showing  fine  bedding 
laminae  and  a  slight  schistosity  parallel  to  the  bedding.  In  the  Cundy 
ore,  which  is  of  this  kind,  there  is  considerable  magnetite  intermingled 
with  the  hematite.  For  this  reason  it  is  much  harder  and  denser  than  the 
(Other  ones  of  this  class  and  has  a  black,  rather  than  a  bluish-black,  color. 
At  the  Keel  Ridge  mine  the  ore  is  platy  and  schistose.  Thin  layers  of 
a  denser  black  hematite  alternate  with  thicker  beds  of  a  finely  granular 
sandy  ore  in  which  there  is  apparently  much  silica  in  the  form  of  sand 
grains.  The  sandy  constituent  has  a  slightly  pink  tinge,  and  since  this  is 
one  of  the  principal  components  of  the  ore  this  too  possesses  a  pinkish 
tinge.     In  the  trade  this  ore  is  sometimes  referred  to  as  a  red  slaty  hema- 


ALGONKIAN,  THE  ORES.  375 

tite.  It  is,  however,  quite  different  from  the  soft  red  hematites  of  the 
Gogebic,  the  Mesabi,  and  the  Marquette  ranges. 

The  lean  ores  produced  by  the  partial  replacement  of  the  jasper  of  the 
jaspilites  by  hematite  are  not  so  distinctly  banded  as  those  of  the  first  class, 
although  their  banding  is  still  very  noticeable.  Usually  they  are  more 
lustrous  than  the  latter,  the  newly  deposited  hematite  being  crystalline, 
causing  the  ores  to  sparkle  with  the  reflections  from  the  crystal  faces.  The 
ores  of  this  class  occur  both  in  the  Traders  and  the  Curry  members,  partic- 
ularly in  those  places  where  the  formation  has  been  deformed  by  folding  or 
brecciation. 

The  brecciated  ores  consist  of  large  and  small  fragments  of  ore  and 
jasper  in  a  matrix  composed  of  small  jasper  and  ore  fragments  and  tiny  ore 
grains  cemented  by  a  porous  ore.  Some  of  the  ore  mined  at  the  Clifford 
pit  of  the  Traders  mine  and  much  of  the  Cuff  ore  is  of  this  character.  In 
some  cases,  as  in  the  Norway  open  pit,  small  pieces  of  dolomite  are  occa- 
sionally intermingled  with  the  other  fragments,  and  in  the  cement  is  a 
large  proportion  of  talc  or  serpentine.  This  type  of  ore  has  usually  a 
reddish  or  purplish  tinge,  though  when  the  ferruginous  cement  is  in  large 
quantity  the  ore  closely  resembles  in  general  appearance  the  porous  crys- 
talline ores  of  the  better  grades,  exhibiting  here  and  there  mottlings  due  to 
the  fracturing  of  ore  or  jasper  fragments.  A  third  type  of  the  brecciated 
siliceous  ore  is  a  brecciated  Brier  slate,  in  which  the  comminuted  slate 
cement,  as  well  as  the  fragments,  are  partially  replaced  by  brown  earthy 
hematite.  These  ores  are  purplish  brown  and  lumpy,  and  often  present 
sllckensides  through  the  mass. 

Nearly  all  the  brecciated  ores  containing  slatj^  material,  and  those 
banded  ores  with  which  are  interbedded  thin  layers  of  slate,  are  coated  on 
the  weathered  surfaces  of  their  joint  planes  with  thin  layers  of  a  yellowish- 
green  substance  having  nearly  the  color  of  epidote.  This  is  much  more 
plentiful  along  the  edges  of  certain  layers  than  of  others,  and  is  sometimes 
limited  to  a  single  layer.  When  examined  carefully  a  large  portion  of  this 
coating  is  discovered  to  be  a  vegetable  growth.  Another  portion,  however, 
probably  consists  of  an  aluminous  silicate"  (see  also  pp.  385-386).  It  is 
found  mainly  on  weathered  surfaces  or  along  the  surfaces  of  joint  cracks  to 

aPutnam,  B.  T.,  Notes  on  the  samples  of  iron  ore  collected  in  Michigan  and  northern  Wisconsin: 
Report  on  the  Mining  Industries  of  the  United  States  (exclusive  of  the  precious  metals),  with  special 
investigations  into  the  iron  resources  of  the  Republic,  etc.,  by  Charles  Pumpelly.  Reports  of  the 
Tenth  Census,  vol.  15,  pt.  1,  1886,  p.  449. 


376  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

which  atmospheric  water  has  had  access.  In  many  instances  the  alteration 
has  penetrated  the  slaty  layers  to  some  depth  and  has  given  their  material 
a  yellowish-green  tinge. 

All  the  ores  of  the  classes  described  above  contain  Ijoth  fragmental  and 
chemically  deposited  material.  Much  of  the  hematite  in  the  banded  and 
the  bi-ecciated  ores  is  of  fragmental  origin,  but  with  it  is  a  considerable 
quantity  of  newly  deposited  material.  It  is  probable  that  none  of  these 
deposits  in  their  original  form  would  have  warranted  exploitation.  By 
enrichment,  however,  their  ferruginous  component  was  propoi'tionately 
increased,  and  in  manjr  cases  is  now  in  sufficient  quantity  to  bring  the 
deposits  within  the  limits  of  merchantable  ores.  Since  the  deposit  of  iron 
oxide  in  these  instances  is  dependent  on  the  same  processes  that  gave  rise 
to  the  rich  ores  that  constitute  the  most  valuable  deposits  of  the  district,  the 
laws  governing  the  distribution  of  the  lean  ores  is  the  same  as  that  deter- 
mining the  positions  of  the  rich  deposits  (see  pp.  392-401).  The  lean  ores, 
like  the  rich  ores,  are  found  in  plunging  synclines  and  in  those  portions  of 
the  ore  formation  that  suffered  brecciation,  jointing,  shearing,  close  folding, 
or  other  deformation  that  produced  conditions  which  afforded  oppor- 
tunities for  the  entrance  of  ground  water  into  the  rocks.  Thus  the  lean 
ores  are  usually  found  in  the  lowermost  portions  of  the  Traders  member 
along  its  contact  with  the  Randville  dolomite  (where  slipping  and  brecciation 
has  taken  place),  along  the  straight  limbs  of  folds  in  both  the  Traders  and 
the  Curry  members,  and  in  the  Curry  member  along  troughs  of  synclines. 
The  last  two  positions  are  favorable  for  ore  concentration  to  some  extent, 
but  not  sufficiently  so,  as  a  rule,  for  the  production  of  rich  ores  like  those 
found  at  the  bottoms  of  troughs  in  the  Traders  member  (see  p.  393). 

The  rich  ores  of  the  district  are  confined,  as  far  as  our  jjresent 
knowledge  goes,  to  the  Traders  member  and  to  a  very  few  exceptionally 
favorable  situations  in  the  Curry  member.  They  occur  in  those  portions 
of  the  Traders  member  near  the  contact  with  the  underlying  dolomite, 
especially  where  the  two  formations  are  separated  by  a  layer  of  serpentine 
and  talc,  or  by  beds  of  impervious  slates.  The  richest  deposits  are  in  the 
troughs  of  pitching  synclines.  In  the  CuiTy  member  they  occur  where 
folding  and  brecciation  were  both  severe. 

These  ores  are  usually  bluish-black,  porous,  friable,  fine-grained 
aggregates  of  crystallized  hematite.  They  crush  easily  and  soil  the  fingers 
when  handled.     They  are  commonly  called  soft  blue  hematites. 


ALGONKIAN,  THE  ORES.  377 

lu  many  cases  the  ores  are  entirely  devoid  of  all  evidences  of  bedding-. 
These  varieties  are  frequently  penetrated  by  tiny  seams  of  dense  hard  ore, 
and  are  cracked  and  gashed  by  openings  that  widen  out  into  distinct 
cavities.  All  surfaces  are  covered  with  druses  of  minute  hematite  crystals, 
which  reflect  the  light  from  thousands  of  sparkling  faces.  Usually,  however, 
the  ores  are  distinctly  laminated.  In  these  the  drusy  character  is  lacking. 
The  ores  are  soft,  and  are  earthy  in  luster  except  where  they  have  suffered 
shearing.  At  such  places  they  become  more  or  less  specular.  Gradations 
between  the  laminated  and  the  massive  ores  are  common.  In  many  of  the 
ores  dense  laminae  and  earthy  or  drusy  ones  alternate,  producing  an  ore 
with  a  platy  structure  which,  when  not  deformed,  splits  readily  between  the 
laminae  into  flat,  clinkery  slabs.  The  dense  laminae  are  vein-like  in 
character  and  appear  to  have  been  introduced  after  the  earthy  ones  had 
attained  their  present  features.  At  the  Ludington  shaft  of  the  Chapin  mine 
much  of  the  ore  is  also  platy.  But  in  this  instance  the  structure  is  due  to 
the  fact  that  laminae  of  the  soft,  earthy,  bluish  hematite  alternate  with 
others  composed  very  largely  of  calcite  or  dolomite.  Between  these  sepa- 
ration occurs  very  readily. 

At  the  ends  of  folds  and  at  a  few  other  places  where  the  iron  formation 
has  been  greatly  shattered  the  ores  are  often  brecciated  and  their  fragments 
cemented  together  by  a  drusy  mass  of  ferruginous  calcite  or  dolomite  or 
by  a  mass  of  porous,  drusy  hematite  identical  in  appearance  with  the 
material  of  the  drusy  ores  referred  to  above.  The  cavities  still  remaining 
in  these  breccias  are  often  partially  filled  with  earthy  brown  limonite,  or 
their  walls  are  coated  by  little  crystals  of  red  siderite.  The  material  of 
the  ore  fragments  in  the  hematitic  breccias  is  like  that  of  the  hematite 
bands  interstratified  with  the  jasper  bands  in  the  jaspilites.  Those  in  the 
calcareous  breccias  are  fragments  of  the  banded  rich  ores  described  in  the 
preceding  paragraph.  In  the  latter  the  replacement  of  silica  by  hematite 
had  practically  been  completed  before  the  ore  was  brecciated,  while  in 
the  former  deposition  of  ore  continued  after  brecciation. 

The  ore  of  the  Curry  shaft  is  so  unlike  any  other  ore  of  the  district 
that  it  deserves  at  least  another  brief  mention  in  this  place  (see  also  pp.  347— 
348).  As  it  appears  on  the  stock  pile  (1899)  most  of  it  is  a  dark-blue,  dense, 
massive  variety  cut  by  veins  of  white  and  dark-red  dolomite  and  contain- 
ing here  and  there  through  it  large  and  small  nests  of  the  same  mineral. 


378  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Other  pieces  are  mottled  in  gray,  pink,  and  yellow  colors.  These  varieties 
are  minutely  brecciated  by  ramifying  veinlets  of  the  carbonate.  While 
these  ores  may  be  enriched  to  some  extent  by  the  deposition  of  hematite 
from  solutions  passing  through  a  lean  ore,  their  present  value  is  due  largely 
to  the  replacement  of  their  original  silica  by  carbonates. 

CHEMICAL    COMPOSITION. 

The  ores  mined  in  the  Menominee  range  during  1900  were  all  Besse- 
mer, with  the  exception  of  one  grade  obtained  from  the  Quinnesec  mine 
and  the  ores  of  the  Walpole  and  the  Cundy  mines.  The  Gundy  ore 
contains  a  large  proportion  of  magnetite,  but  the  ferruginous  component 
of  all  the  other  ores  is  almost  exclusively  hematite,  although  all  contain 
magrnetite  to  some  extent.  This  varies  in  amount  between  1.51  and  9.56 
per  cent "  in  the  di'ied  ores,  of  which  complete  analyses  have  been  pub- 
lished. The  purest  hematite  being  shipped  contains  about  92  per  cent 
of  Fe203.  In  addition  to  the  iron  oxides  all  the  ores  contain  varying 
amounts  of  SiOn,  AI2O3,  CaO,  MgO,  COo,  S,  P2O5,  and  HjO,  and  most  of 
them  also  some  manganese,  KgO  and  NagO.  In  a  few  ores  Ti02  and  C 
have  been  detected. 

The  minimum  silica  reported  in  the  ores  of  1900  is  2.75  per  cent. 
The  average  in  the  richer  ores  is  about  4  per  cent.  The  maximum  limit 
of  this  constituent  fluctuates  with  the  ore  market,  since  an  increase  in  silica 
means  a  decrease  in  the  metallic  contents,  and  a  consequent  decrease  in 
market  value.  In  1900  the  maximum  silica  was  38.65  per  cent  in  an  ore 
containing  40.93  per  cent  Fe  (equivalent  to  5§.46  Fe203).  The  AI2O3  varied 
between  0.61  per  cent  and  1.89  per  cent,  the  CaO  between  0.18  per  cent 
and  1.58  per  cent,  and  the  MgO  between  0.21  per  cent  and  3.35  per  cent. 
Manganese  was  found  in  the  averages  of  all  the  cargo  analyses  of  1900,  in 
quantities  between  0.08  per  cent  and  0.43  per  cent,  corresponding  to  0.10 
per  cent  and  0.55  per  cent  MnO,  but  in  some  of  the  specimens  collected  by 
the  agents  of  the  Tenth  Census  it  was  not  detected,  or,  at  any  rate,  it  was 
not  reported. 

Sulphur  and  phosphorus  are  universally  present,  but  neither  exists  in 

«  Fifteen  complete  analyses  of  Menominee  ores  are  published  in  the  Reports  of  the  Tenth 
Census,  vol.  15,  1886,  pp.  437-153.  While  it  is  not  pretended  that  these  analyses  represent  exactly  the 
ores  shipped  at  present,  nevertheless,  they  probably  indicate  the  character,  and,  approximately, 
the  degree  of  variation  in  the  composition  of  these  ores. 


ALGONKIAN.  THE  ORES.  379 

any  considerable  quantity.  The  former  element  is  present  between  tiie 
limits  0.002  per  cent  and  0.028  per  cent,  corresponding  to  0.0036  per  cent 
and  0.05  per  cent  FeSj,  and  phosphorus  between  0.009  per  cent  and  0.135 
per  cent,  corresponding  to  0.U2  per  cent  and  0.3105  per  cent  P2O5. 

Records  of"  the  percentages  of  the  other  components  present  are  not  to 
be  found  in  the  recently  published  anah^ses.  In  those  of  the  Tenth 
Census,  however,  they  are  given,  and  the  determinations  seem  to  have 
been  made  with  great  accuracy.  In  recent  analyses  the  loss  on  ignition  is 
specifically  stated  (it  varies  between  0.65  per  cent  and  3.24  per  cent),  but 
the  proportion  of  this  loss  due  to  the  escape  of  COo  is  not  recorded.  In  the 
Census  analyses  CO2  was  detected  in  every  sample  analyzed,  in  quantities 
usually  varying  between  0.08  per  cent  and  0.50  per  cent.  In  one  oi-e, 
however,  that  froin  the  old  Keel  Ridge  mine  in  the  northwest  quarter  of 
the  southeast  quarter  of  sec.  32,  T.  40  N.,  R.  30  W.,  the  proportion  was 
7.12  per  cent.  No  description  of  this  ore  is  given  in  the  report,  but  it 
was  probably  cut  by  veins  of  dolomite  like  the  ore  of  the  Curry  mine, 
which  contains  22  per  cent  of  dolomite  (see  p.  348),  or  was  an  ore  in 
which  the  quartz  had  been  replaced  by  a  carbonate,  like  some  of  the  ore 
from  the  Chapin  mine.  The  ores  in  which  the  CO2  was  present  in  small 
quantity  probably  contained  the  substance  in  calcite  (0.18  per  cent  to  1.14 
per  cent)  scattered  through  them  in  little  nests  (see  p.  314) 

Of  the  alkalies  K3O  was  found  in  11  of  the  15  samples  analyzed  and 
NaoO  in  5  of  them,  but  since  these  constituents  were  sought  for  only  in 
those  cases  in  which  the  sum  of  the  other  constituents  amounted  to  less  than 
100  per  cent,  it  is  probable  that  they  occur  in  a  larger  proportion  of  the  ores, 
if  not  in  all.  The  KoO  was  present  between  the  limits  0.05  per  cent  and  2.29 
per  cent,  and  the  NajO  between  0.02  per  cent  and  0.30  per  cent.  Carbon 
was  detected  three  times  in  small  quantities,  viz,  0.006  per  cent  twice  and 
0.01  per  cent  once,  and  TiOg  in  one  sample  to  the  amount  of  0.075  per  cent. 
It  was  present  in  several  other  samples  as  traces  too  small  to  be  determined. 

The  specific  gravity  of  the  ores  is  dependent  partly  upon  thf  V  compo- 
sition and  partly  upon  their  physical  structure.  A  large  number  of  deter- 
minations were  carefully  made  by  the  chemists  of  the  Tenth  Census." 
These  showed  a  very  wide  range,  i.  e.,  between  3.447  and  5.173,  but  their 

"  Reports  Tenth  Census,  vol.  15,  1886,  pp.  531-535. 


380 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


value  was  in  no  wise  comparable  with  the  iron  contents  of  the  samples,  as 
the  following  short  tabular  exhibit  will  affirm: 


Density  of  JL 


enoinm 


>,ee  ores  corwpared  with  iron,  contents. 


Mine. 


Density. 


Breen  . 
Cyclopi 
Norwa; 
Breen  . 


3.447 
S.  478 
3.830 
4. 590 


Iron. 


50.17 
64.38 
59.72 
59.79 


Mine. 


Curry 

Quinnesee 
Vulcan  . . . 
Currv 


Density. 


5.001 
5.006 
5.  036 
5.173 


67.40 
63.49 
67.62 
67.  53 


The  great  variation  in  the  structure  of  the  ores  is  also  responsible  for 
great  variations  in  their  capacity  for  absorbing  water  and  retaining  it.  The 
ore  as  it  comes  from  the  mine  is  saturated  with  moisture.  That  removed 
from  the  mine  and  protected  from  the  rain  for  a  long  time  becomes  diy, 
and  on  analysis  yields  only  a  trace  of  water.  That,  however,  which 
remains  unprotected  on  stock  piles,  and  ore  in  transit,  absorbs  such  a  great 
quantity  of  water  that  it  is  a  matter  for  serious  consideration  whether  it 
would  not  prove  profitable  to  dry  it  before  shipment  and  protect  it  during 
transportation  to  the  furnaces.  The  average  cargo  analyses  showed  the  ores 
in  1900  to  contain  in  their  natural  state,  i.  e.,  before  drying,  percentages  of 
moisture  varying  between  2.10  and  8.97,  the  lean  ores  as  a  rule  showing 
less  moisture  than  the  richer  ones,  mainly  because  of  their  less  porous 
character.  In  the  table  below  the  moisture  contents  of  some  of  the  ores 
are  indicated.  The  figures  do  not  represent  percentage  weights  of  the  dry 
ores,  the  analyses  of  which  are  given  above  the  moisture  figures,  but  they 
are  moisture  percentages  based  on  the  weights  of  the  natural  ores,  i.  e.,  of 
the  dry  ores  plus  the  moisture,  and  therefore  are  considerably  smaller  than 
they  would  be  if  calculated  on  the  weights  of  the  former.  The  shipments 
of  one  mine  alone  in  1899  contained  over  58,000  tons  of  water  in  addition 
to  that  which  was  chemically  combined  in  its  constituents. 

In  the  following  table  the  average  cargo  analyses  of  some  of  the  ores 
shipped  in  1899  are  arranged  in  the  order  of  diminishing  silica.  While  it 
is  recognized  that  the  composition  of  the  individual  ores  varies  from  year 
to  year,  nevertheless  the  general  features  exhibited  by  their  analyses  remain 
practically  the  same.  The  figures  for  1899  are  chosen  rather  than  those  of 
later  seasons,  because  the  former  correspond  to  the  ores  described  in  the 


ALGONKIAN,  THE  ORES.  381 

foregoing  paragraphs.  The  analyses  are  not  so  complete  as  those  published 
by  the  Tenth  Census,  but  they  furnish  abundant  data  for  comparison  of  the 
different  grades  and  give  an  excellent  summary  of  their  characters. 

The  results  are  calculated  on  the  weights  of  samples  dried  at  212°  F. 
The  moisture  figures  represent  the  loss  of  weight  in  drying  and  are  calcu- 
lated as  percentages  of  weight  of  the  natural  ores  before  drying.  The  iron 
is  calculated  as  FcaOg,  although  it  is  probable  that  in  every  instance  some 
of  it  is  in  the  form  FegOi.  Except  where  otherwise  indicated,  the  analyses 
are  taken  with  slight  modifications  from  Mineral  Resources  of  the  United 
States,  1899,  Twenty -first  Annual  Report  U.  S.  Greological  Svirvey,  Part 
VI,  pages  39-40. 


382 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


5- 

51 


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ALGONKIAN,  THE  ORES. 


383 


Of  the  four  analyses  given  below,  the  first,  made  from  a  sample  of  the 
Chapin  ore,  was  furnished  by  Mr.  E.  E.  Brewster.  The  second  and  third 
are  analyses  of  two  grades  of  "soft  specular"  Quinnesec  ore,  and  the  fourth 
of  a  "soft  specular"  blue  ore  from  the  Cornell  mine.  The  last  three 
analyses  are  taken  from  the  Tenth  Census  Rei:)ort.  They,  of  course,  do 
not  represent  the  exact  composition  of  any  ores  being  mined  at  the  j^resent 
time,  but  they  afford  the  best  data  we  have  for  determining  the  mineral 
composition  of  the  richer  of  the  Menominee  ores,  and  for  this  reason  they 
are  quoted.  The  second  analysis  was  made  from  chips  selected  with  special 
reference  to  securing  a  sample  rich  in  the  greenish-yellow  incrusting  mineral 
(see  p.  375)  that  coats  the  ore-bearing  rocks  in  many  places. 

Complete  analyses  of  Ohapin,  Quinnesec,  and  Cornell  ores. 


I. 

II. 

III. 

IV. 

Fe 

60.54 

55.58 

65.63 

57.03 

FejOa  

85.44 
.47 

1.33 
.76 

1.26 

3.02 
.064 
.066 

4.53 
.15 
.002 

76.14 
2.87 
4.69 

91.51 
1.97 
1.53 

80.15 
1.10 
3.88 

FeO 

AloOa 

MnA 

CaO 

.27 
3.55 

.99 

.02 
9.31 

.021 
FeS2=  .110 

.30 
1.72 

.36 
.21 
.  57 
.03 
3.03 
.021 
.099 
.38 
.27 

.17 
.48 
2.29 
.30 
10.72 
.074 
.146 
.08 
.56 

MgO 

KjO 

Na.,0 

SiOj 

PA 

S . 

CO, 

HjO  (above  100° ) 

2.75 

Total 

99. 842 

99. 991 

99.  980 

99. 950 

384 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


Ill  the  course  of  the  analyses  of  the  Quiiinesec  and  Cornell  ores  the 
insoluble  components  were  determined  separately,  with  these  results: 

Insoluble  constituents  of  Quinnesec  and  Cornell  ores. 


II. 

III. 

IV. 

Total  insoluble 

12.02 

4.61 

16.45 

giOj                                                               - 

9.31 

1.61 

.09 

.09 

.93 

3.03 
.93 
.07 

.06 
..51 
.03 

10.72 

A1„0=                                              

3.21 

CaO                                                - 

MeO                                                 

.08 

K„0                                              

2.23 

Na^O                                           . .  ^ 

.20 

Xotal                                                        

12.03 

4.63 

16.44 

MINERALOGICAL    COMPOSITION. 


MINERAL    CON.STITUENTS    OF    THE    ORES. 


From  the  microscopical  examination  of  the  ores  it  is  learned  that  they 
contain  hematite,  magnetite,  quartz,  calcite,  dolomite,  muscovite,  and  ser- 
pentine. The  chemical  analyses  show,  in  addition,  the  presence  of  pyiite, 
apatite,  and  some  manganiferous  mineral.  All  of  these  minerals  appear  to 
occur  in  practically  all  the  ores,  but  they  are  found  in  greatly  varying 
amounts.  In  attempting  to  calculate  their  proportions  in  the  ores,  the  analyses 
of  which  are  given  above,  we  are  met  by  several  difficulties  which  can  not 
be  entirely  overcome.  In  the  first  place,  no  microscopical  examination  was 
possible  in  the  case  of  any  of  the  samples  analyzed.  Hence  there  is  no 
knowing  whether  all  the  minerals  mentioned  above  were  in  these  samples 
or  not;  or,  if  all  were  jDresent,  which  of  the  rarer  ones  were  in  excess.  In 
analysis  I  there  was  no  determination  of  CO2  separately  from  H2O,  though 
it  was  known  to  be  present.  In  sample  II  there  was  presumably  present 
some  serpentine  in  addition  to  the  yellowish-green  mineral,  which  is  prob- 
ably a  soluble  silicate  of  magnesia  and  alumina.  But  there  is  nothing  to 
guide  in  the  distribution  of  the  ALOa,  MgO,  and  SiOa  between  these  minerals, 
or  in  determining  how  much  of  the  bases  occur  in  them  and  what  proportions 
are  present  as  isomorplious  mixtures  in  the  hematite  and  magnetite.  If  we 
assign  all  the  P2O5  to  apatite,  all  the  COo  to  dolomite,  all  the  FeO  to  mag- 
netite, and  the  insoluble  K2O,  NajO,  and  AI2O3  to  muscovite,  calculate  the 


ALGONKIAN,  THE  ORES. 


385 


proportion  of  MgO  necessary  to  unite  with  the  available  CaO  in  the 
formation  of  dolomite,  and  assign  the  balance  to  serpentine,  the  mineral 
composition  of  the  first,  third,  and  fourth  of  the  above  ores  is  as  indicated 
below : 

Min&ral  constituents  of  rick  ores. 


Hematite  (Fe203  + AlA)  • 

Magnetite 

I\Iusco\'ite 

Serpentine 

Dolomite 

Apatite 

Pyrite 

Quartz  (excess  of  SiOj)  ... 

Manganite  (?)  

Excess  unaccounted  for: 

H2O 

K,0 


Na^O . . . 
Total. 


85.55 
1.51 

.54 
6.49 
2.62 

.35 

.004 
1.46 

.85 

.48 


99.  854 


III. 


87.74 

6.  .34 

2.62 

.25 

.82 

.048 

.099 

1.84 


IV. 


.17 


.03 


99. 957 


78.28 

3.54 

9.45 

1.15 

.18 

.171 

.146 

6.  50 


..32 
.06 
.10 


99. 897 


It  is  fully  realized  that  the  above  estimates  are  only  approximate.  In 
the  calculations  all  the  CaO  in  excess  of  that  required  by  the  P2O5  to  form 
apatite  is  assigned  to  the  dolomite,  and  enough  MgO  in  addition  to  saturate 
the  CO2.  The  remaining  MgO  is  all  considered  as  occun-ing  in  serpentine. 
If  the  dolomite  is  richer  in  MgO  than  it  is  assumed  to  be,  the  percentages 
of  the  serpentine  in  the  ores  are  less  than  estimated  and  the  percentages  of 
quartz  larger.  Moreover,  the  excess  of  CaO  which  would  then  be  unac- 
counted for  would  probably  indicate  the  presence  of  some  chlorite.  Again, 
some  of  the  magnesia  may  be  in  the  form  of  talc,  but  that  this  mineral  is 
present  to  any  considerable  amount  is  not  probable,  since  talc  contains  less 
water  than  serpentine,  and  even  on  the  assumption  that  all  the  MgO  is  in 
serpentine  there  is  nevertheless  some  water  unaccounted  for  in  every  analy- 
sis. Serpentine  is  an  abundant  constituent  in  some  of  the  ores,  as  will  be 
shown  later. 

If  we  exclude  from  consideration  the  MgO  in  analysis  II  and  distrib- 
ute the  other  oxides  in  the  same  manner  as  was  done  in  the  remaining  three 
MON  XLVI — O-t 25 


386  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

analyses,  the  calculated  percentages  of  the  mineral  components  become: 
Hematite,  69.77;  mag-netite,  9.24;  muscovite,  4.55 ;  dolomite,  0.64;  apatite, 
0.048;  and  pyrite,  0.110.  This  would  leave  3.08  per  cent  AI2O3,  3.45  per 
cent  MgO,  7.41  per  cent  SiOg,  and  1.61  per  cent  HjO  to  be  distributed 
among-  the  serpentine  or  talc,  quartz,  and  the  yellowish-green  incrusting 
mineral.  If  all  the  MgO  is  assumed  to  be  present  as  serpentine,  there 
would  be  required  3.72  per  cent  SiOg  and  1.22  per  cent  HjO  to  combine 
with  it,  leaving  3.08  per  cent  ALOg,  0.39  per  cent  HgO,  and  3.69  per  cent 
Si02  (3=2  AI2  SisOT  +  lJ  H.2O)  to  represent  the  quartz  and  the  yellowish- 
gi'een  incrustation.  According  to  this  calculation,  however,  the  serpentine 
would  be  in  an  excessive  amount,  i.  e.,  8.39  ]jer  cent,  which  is  not  thought  to 
be  })rolja-ble.  Evidently  the  greenish-yellow  mineral  is  a  soluble  aluminous 
silicate,  but  whether  it  contains  much  or  little  MgO  can  not  be  learned  with 
the  data  at  present  in  hand. 

Of  course  the  lean  ores,  since  they  contain  a  much  higher  percentage 
of  silica  than  the  rich  ores,  the  analyses  of  which  are  quoted  above,  must, 
in  consequence  of  this  fact,  contain  smaller  proportions  of  the  other  con- 
stituents. Moreover,  since  many  of  them  are  but  slightly  changed  phases  of 
the  normal  jaspilites,  they  contain  but  small  proportions  of  talc,  serpentine, 
calcite,  dolomite,  and  other  minerals  that  were  deposited  by  the  circulating 
waters  by  whose  action  the  richer  ore  bodies  were  concentrated.  Otherwise 
the  lean  ores  are  similar  to  the  richer  ones.  Both  kinds  are  composed  of  the 
same  chemical  elements,  but  they  contain  them  in  different  proportions. 

MINERALS   ASSOCIATED   WITH   THE  ORES. 

All  the  minerals  mentioned  above  as  being  constituents  of  the  ores 
are  occasionally  visible  in  the  hand  specimens,  with  the  exception  of  the 
apatite. 

Quartz,  dolomite,  and  calcite. — Quartz,  dolomite,  and  calcite  appear  in 
veins  cutting  the  ores,  as  has  already  been  repeatedly  stated.  The  quartz 
and  calcite  are  nearly  always  in  small  veins,  most  of  which  are  straight, 
marking  the  positions  of  joint  cracks.  The  dolomite  is  also  usually  in 
small  veins,  but  sometimes  the  veins  are  2  or  3  inches  in  width.  The 
smaller  veins,  like  most  of  the  quartz  veins,  mark  the  positions  of  joints. 
The  larger  veins,  however,  cut  across  the  bedded  ores  in  any  direction,  but 
most  frequentlv  penetrate  them  along  their  bedding  planes.     The  quartz 


ALGONKIAN.  THE  ORES. 


387 


Fig.  28.— Calcite  crystal  of  second  type,  in  ore 
of  West  Vulcan  mine. 


and  calcite  are  usually  white.     The  dolomite  is  either  white  or  of  a  dark- 
pink  color. 

Dolomite  in  small  brownish-yellow,  flat,  rhombohedral  crystals  with 
rounded  faces  also  forms  druses  lining  cavities  and  vugs  in  the  ore.  This 
variety  and  the  pink  vai'iety  are  doubtless 
strongly  ferruginous.  The  former  may  ap- 
proach siderite  very  closely.  Often  calcite 
is  associated  with  the  dolomite  in  druses,  the 
former  appearing  in  transparent  or  translu- 
cent scalenohedra  or  highly  modified  rhombo- 
hedi'a,  and  the  latter  as  opaque  white  simple 
rhombohedra  with  curved  faces.  Sometimes 
the  dolomite  crystals  are  implanted  upon 
those  of  calcite;  at  other  times  the  two  are 
intermingled  promiscuously.  In  many  cases 
calcite  occurs  also  alone  in  druses  covering- 
the  walls  of  pores  and  in  crystallized  aggre- 
gates constituting  the  cement  of  ore  breccias. 

In  many  instances  the  calcite  crystals  are  well  developed  and  of  large 
size.     In  the  West  Vulcan  and  a  few  other  mines  water  channels  runninff 

through  the  ore  are  lined  with  numerous  white  cal- 
cite crystals,  some  of  which  are  of  great  beauty.  In 
the  West  Vulcan  mine  the  crystals  often  mea,sure 
three-fourths  of  an  inch  in  length  and  one-fourth 
inch  in  diameter.  They  are  of  three  types.  The 
first  type  consists  of  a  steep  scalenohedrt)n  made 
uj)  of  many  subindividuals.  The  second  type  is  a 
steep  rhombohedron,  approaching  16  R,  terminated 
by  —  1/2  R  (fig.  28),  and  the  third  type  a  combi- 
nation of  these  two  forms  with  a  steep  positive  scale- 
nohedron  that  is  approximately  4/7  R  5/2  (see  fig.  29). 
The  —  1/2  R  and  planes  of  the  scalenohedron  are 
always  striated  by  lines  parallel  to  the  intersections 
of  these  planes  with  a  positive  rhombohedron  which  truncates  their  solid 
angles  and  the  planes  of  16  R  by  curved  lines  approximating  correspondino- 
directions. 


Fig.  29.— Calcite  crystal  of  third 
type,  in  ore  of  West  Vulcan 
mine. 


388  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Ill  some  places  the  crystals  are  implanted  directly  upon  a  breccia  of 
ore  and  jasper  fragments.  In  other  places  they  cover  a  layer  of  red  ocher 
which  is  about  one-half  inch  thick,  lying  upon  the  breccia  and  separating 
it  from  the  calcite.  Again,  in  still  other  places  the  crystals  are  implanted 
directly  upon  banded  jaspilite.  Sometimes  the  jaspilite  is  replaced  by 
pyrite  forming  a  finely  granular  mass  in  which  the  original  bedding  lines 
can  still  be  detected,  and  the  calcite  crystals  are  attached  to  this. 

Pyrite  and  clmlcopyrite. — In  many  instances  the  calcite  occurs  alone  on 
the  walls  of  the  water  course,  but  frequently  there  are  associated  with  it 
a  large  quantity  of  pyrite  and  some  chalcopyrite.  The  pyrite  appears  on 
the  whole  to  be  older  than  the  calcite,  although  the  two  minerals  are  in 
most  cases  so  intimately  associated  that  they  must  have  been  deposited 
nearly  simultaneously.  The  chalcopyrite  is  also  older  than  the  calcite,  but 
its  age  with  respect  to  the  pyrite  is  not  known,  as  the  two  sulphides  have 
not  been  seen  together. 

Both  the  sulphides  also  form  coatings  on  the  ore,  ranging  in  thickness 
from  a  small  fraction  of  an  inch  to  an  inch  or  more.  The  pyrite,  more- 
over, occurs  as  isolated  crystals  implanted  on  the  ore  and  embedded 
among  the  calcite  crystals,  and  occasionally  as  separate  grains  disseminated 
through  the  jaspilite  within  a  distance  of  an  inch  or  more  from  the  walls  of 
cavities  The  coatings  are  in  a  few  instances  mammillary,  but  in  most 
cases  they  are  crystalline.  When  broken  their  inner  portions,  of  course, 
appear  massive,  but  their  outer  surfaces  are  made  up  of  crystals,  which  in 
the  pyrite  are  excellent  combinations  of  the  cube  and  octahedron,  and  in  the 
chalcopyrite  are  combinations  of  tetrahedrons.  The  chalcopyrite  crystals 
are  rarely  more  than  a  few  millimeters  in  diameter.  Their  faces  are  rough 
and  many  of  them  are  built  up  by  parallel  growths  of  smaller  individuals. 
The  pyrite  crystals  are  larger.  Many  measure  8  mm.  on  an  edge.  All  are 
bright  and  their  planes  are  well  developed. 

Other  minerals  in  joint  cracks. — The  calcite,  dolomite,  siderite,  and  pyrite 
are  found  in  druses  so  abundantly  and  in  the  ores  and  associated  jaspilites 
at  so  many  different  places  that  they  may  safely  be  regarded  as  universal 
accompaniments  of  the  ores.  In  addition  to  these  minerals,  there  are  often 
found  covering  the  walls  of  joint  cracks  in  the  ores  and  jaspilites  of  the 
Chapin  mine,  according  to  Mr.  Brewster,  druses  of  feldspar  and  of  rhodo- 
chrosite,  and,  occasionally  in  the  slates  associated  with  the  ores,  druses  of 


ALGONKIAN,  THE  ORES.  389 

mang-anite  and  barite.  The  joint  surfaces  of  the  slates  taken  from  the 
Pewabic  mine  are  also  in  rare  instances  covered  with  a  thin  coating  of  a 
soft,  dark-green  mineral  that  gives  the  blowpipe  tests  for  chromium  and 
water.  It  has  been  found  in  such  sniall  quantities  that  a  satisfactory  deter- 
mination of  its  nature  has  not  yet  been  possible.  In  the  only  specimen 
seen  by  the  writer  the  mineral  occurred  as  a  thin,  soft,  flaky  coating  devoid 
of  all  traces  of  crystallization.  It  appeared  more  like  a  chromiferous 
chlorite  than  anything  else. 

Serpentine. — Ser^^entine,  as  has  been  stated,  occurs  almost  universally 
in  the  ores,  but  usually  in  such  small  quantities  as  not  to  be  noticeable  in 
the  hand  specimen.  Frequently,  however,  it  can  be  detected  as  small  gray 
or  white  particles  scattered  so  uniformlj^  through  the  ores  as  to  give  them  a 
grayish  tinge.  It  appears  to  be  more  plentiful  in  the  lower  than  in  the 
upper  portions  of  the  deposits.  This  fact,  together  with  the  further  fact 
that  in  the  Chapin  mine  the  ore  from  the  upper  portions  of  the  lenses  is 
more  porous  than  that  from  their  lower  portions,  suggests  that  the  mineral 
has  been  deposited  by  downward  percolating  waters  and  has  accumulated 
near  the  impervious  basements  at  the  bottoms  of  the  ore  deposits.  At 
some  places  in  the  Chapin,  the  West  Vulcan,  and  other  mines,  the  serpen- 
tine occurs  in  large  masses  within  the  ore  and  along  water  channels, 
sometimes  alone  and  sometimes  associated  with  calcite  crystals.  In  many 
cases  the  walls  of  cavities  are  covered  with  calcite  and  their  interiors  filled, 
or  partially  filled,  with  serpentine,  forming  geodes  with  serpentine  fillings. 
Eectangular  masses  of  the  mineral,  almost  ideally  pure,  have  been  seen  by 
the  writer  which  measure  5  inches  along  an  edge.  Undoubtedly  much 
larger  masses  occur  in  the  mines.  The  mineral  is  amorphous.  It  varies  in 
color  from  dark  pink  to  snow  white,  the  darker  varieties  being  more 
prevalent  in  cracks  and  fissures  in  the  jaspilites  and  the  white  varieties  in 
the  geodes  and  along  water  courses  lined  by  calcite.  In  some  specimens 
of  the  darker  varieties  distinct  and  definite  bedding  lines  may  be  noted. 

The  analysis  by  Mr.  Brewster  of  a  white,  soapy  variety  from  the 
Chapin  ore  places  the  identity  of  the  material  beyond  question. 


390 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Analysis  of  minerals  from  the  Chajnn  ore. 


Serpentine. 

Talc. 

Found. 

Calculated  for 
HillgsSioO,. 

Found. 

Calculated  for 
H,Mg3SiiO,». 

SiOj 

42.99 

1.18 

1.40 

.30 

43.  48 

61.91 

1.06 

.39 

.14 

Tr. 

32.  52 

4.39 

63.49 

AlA 

FejOs 

MnA 

CaO 

MgO 

39.84 
14.08 

43.48 
13.04 

31.75 

H.,0 

4.76 

Total 

99.79 

100. 00 

100. 41 

100. 00 

Talc. — Another  white  mineral  coating  slickensided  surfaces  in  the 
jaspilites  and  the  underlying  slates,  and  filling  crevices  in  the  latter,  diiFers 
from  the  serpentine  in  being  softer,  having  a  greasy  feel,  and  in  having  an 
obscurely  flaky  structure.  Its  specific  gravity  is  2.72.  From  Mr.  Brewster's 
analysis  given  above,  this  mineral  is  seen  to  be  talc.  It  appears  to  be  less 
abundant  in  the  ores  than  the  serpentine,  but  is  very  common  in  the  slates 
underlying-  them.  Flat  pieces  measuring  three-fourths  of  an  inch  in 
thickness  and  3  or  4  inches  in  length  and  breadth  have  been  picked  from 
the  dump  heaps  of  some  of  the  mines,  but  in  no  case  were  any  substances 
attached  to  the  specimens  that  would  help  to  discover  the  paragenesis  of 
the  mineral.  In  every  case  the  specimen  seemed  to  have  come  from  a 
crevice. 

Since  talc  and  serpentine  are  found  so  frequently  along  slickensides  in 
the  dolomite,  and  since  great  deposits  of  them  occur  also  in  the  contact 
between  this  rock  and  the  overlj-ing  Vulcan  beds  where  slipping  between 
the  two  series  has  taken  place,  the  inference  seems  to  be  warranted  that 
the  mao-uesia  of  these  minerals  was  derived  from  the  dolomite  and  that  the 
silicates  were  deposited  by  percolating  Avater.  The  lime  of  the  original 
rock  was  carried  farther  and  was  deposited  in  the  pores  and  open  spaces  of 
the  ores  as  calcite. 

'Efflorescence  on  ores. — Whenever  the  ores  are  exposed  to  the  weather 
in  stock  piles  or  the  associated  ferruginous  slates  are  left  exposed  in  dump 
heaps  for  any  considerable  length  of  time  (six  months  or  more),  they 
become  coated  with  a  white  efflorescence.     In  wet  weather  this  washes  ofiP, 


ALGONKIAN,  THE  ORES. 


391 


but  it  accumulates  again  in  dry  weather,  and  on  large  specimens  the 
thickness  of  the  coating  increases  with  the  duration  of  the  dr)-  spell.  Mr. 
Brewster  has  also  analyzed  this  material  with  the  following  result: 

Analysis  of  efflorescence  07i  the  ores. 


Found. 

Gypsum. 

MgSOi+HoO 

Residue. 

Residue, 

exclusive  of 

water. 

Calc.  for 
Na^SOj. 

CaO 

0.74 

.79 

.24 

40.58 

54.01 

3.05 

0.74 

MgO 

0.79 

K.,0 

0.24 
40.58 
51.37 

2.21 

0.26 
44.02 
55.  72 

1           43.7 

Na^O 

SO3 

1.06 
.48 

1.58 
.36 

56.3 

HjO ^... 

Total 

99.41 

2.28 

2.73 

94.40 

100. 00 

100. 00 

In  the  course  of  the  analysis  the  material  was  washed  from  the  ore  and 
dried.  The  determination  of  the  water  does  not,  therefore,  represent  the 
water  content  of  the  original  mineral,  but  simply  the  quantity  of  water 
left  in  it  after  solution  and  desiccation.  The  principal  mineral  in  the 
coating  is  probably  mirabilite  (NaaSOi+lOHoO),  which  is  known  to  become 
dehydrated  upon  heating  or  upon  exposure  to  the  air.  Its  genesis  is 
probably  as  follows:  The  pyrite  in  the  ores  when  exposed  to  the  air  and 
rain  becomes  oxidized  and  jjroduces  sulphuric  acid.  This  acts  on  the 
muscovite  or  traces  of  other  sodium-bearing  minerals  (see  analysis  of  the 
ores,  p.  384)  always  accompanying  the  ores,  yielding  NaoSOi,  which  is 
dissolved  in  the  rain  water.  This  solution  is  then  drawn  to  the  drpng 
surfaces  of  the  individual  lumps  by  capillarity.  The  water  escapes  by 
evaporation,  leaving  the  sulphate  as  an  efflorescence  which,  on  further 
drying,  becomes  anhydrous.  The  dolomite  in  the  ore  is  also  dissolved  in 
the  sulphuric  acid,  yielding  calcium  and  magnesium  sulphates,  which  are 
likewise  drawn  to  the  drying  surfaces,  where  they  become  intermingled 
with  the  sodium  sulphates.  These  sulphates,  however,  are  less  soluble 
than  the  sodium  salt  and  hence  are  always  present  in  the  efflorescence  in 
smaller  quantity. 


392  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

THE  ORE  DEPOSITS. 
DISTKIBUTION   AND    SHAPES. 

The  ore  deposits  of  the  Menominee  district  occur  in  the  two  iron- 
beai'ing-  members  of  the  Vulcan  formation:  (1)  The  Traders,  and  (2)  the 
Curry.  The  ores  may  occur  at  any  horizon  within  these  members,  but 
other  conditions  being  equal  they  are  more  likely  to  occur  at  lower  and 
higher  horizons  than  at  middle  horizons.  However,  a  number  of  the  large 
ore  bodies  extend  entirely  across  the  members  in  which  they  occur. 

It  has  been  stated  repeatedly  in  the  preceding  pages,  and  the  reasons 
for  the  statement  will  be  discussed  in  the  following  section,  that  the  ores 
are  largely  water-deposited  material,  consisting  in  part  of  mechanical 
sediments  and  in  part  of  chemical  sediments.  The  enrichment  of  the  ores, 
which  was  necessaiy  to  make  them  sufficiently  ferruginous  to  be  mined 
with  profit,  was  almost  exclusively  a  chemical  process.  Ferriferous  solutions 
penetrated  the  rocks  along  every  crevice,  depositing  hematite  and,  as  will 
be  seen  later,  removing  silica.  Therefore  the  richer  ores  are  found  in 
situations  where  the  attitudes  of  the  I'ocks  are  such  as  to  furnish  converg-ing' 
chaimels  for  percolating  waters,  and  the  largest  deposits  are  in  the  main 
channels  toward  which  the  drainage  converges.  Consequently,  the  deposits 
of  large  size  rest  upon  relatively  impervious  foundations,  which  are  in  such 
positions  as  to  constitute  pitching  troughs.  A  pitching  trough  may  be 
made  (a)  by  the  dolomite  formation  underlying  the  Traders  member  of  the 
Vulcan  formation,  (6)  by  a  slate  constituting  the  lower  part  of  the  Traders 
member,  and  (c)  by  the  Brier  slate  between  the  Traders  and  Curry 
members.  The  dolomite  formation  is  especially  likely  to  furnish  an 
impervious  basement  where  its  upper  horizon  has  been  transformed  into  a 
talc-schist,  as  a  consequence  of  folding  and  shearing  between  the  formations. 

While  all  the  largest  iron-ore  bodies  are  confined  to  the  pitching 
troughs  with  impervious  basements  of  dolomite  or  slate,  smaller  ore  deposits 
occur  at  contacts  between  the  different  members  and  at  places  within  the 
iron-bearing  members  where  severe  brecciation  has  occurred.  The  contacts 
between  adjacent  formations  are  favorable  places  for  the  concentration  of 
ore,  because  they  are  horizons  along  which  important  slipping  or  diff'erential 
movement  has'occun-ed  during  the  folding  of  the  district.  Wherever  a  set 
of  beds  is  folded  there,  must  be  differential  movement  among  the  layers. 


ALGONKIAN,  THE  ORE  DEPOSITS.  393 

This  is  well  illustrated  by  the  slipping  of  the  leaves  of  a  flexible  book  over 
one  another  when  the  book  is  bent.  In  nature  the  contact  planes  between 
formations  of  different  characters  are  always  planes  of  weakness,  hence  at 
such  places  the  major  movements  take  place.  These  movements  are  sure 
to  make  the  formations  porous  and  thus  produce  main  cliannels  for 
percolating-  water,  hence  the  frequent  presence  of  ore  bodies  at  the  contact 
planes.  Small  ore  deposits  are  found  where  faulting  has  occurred  or  where 
close  plication  has  brecciated  the  formations,  because  the  movements  that 
result  in  these  phenomena  produce  zones  or  areas  where  percolating  waters 
are  converged  into  trunk  channels  and  thus  favor  the  concentration  of  the 
iron  oxide. 

The  combination  of  two  or  all  of  these  conditions  is  more  favorable 
than  any  one  of  them  for  the  deposition  of  large  ore  bodies.  Where  the 
conditions  are  such  as  to  combine  pitching  troughs  with  impervious 
basements,  contact  planes  between  formations,  and  faulting  or  brecciation, 
ore  deposits  of  the  first  magnitude  may  be  expected.  Such  are  the 
conditions  at  the  great  mines  in  the  district.  However,  in  the  search  for 
an  ore  deposit,  the  first  of  the  favorable  conditions — a  pitching  trough 
with  an  impervious  basement — is  the  dominant  consideration.  It  can  not 
be  too  strongly  insisted  that  the  essential  condition  for  the  development  of 
a  large  iron-ore  body  in  the  Menominee  district  as  well  as  in  the  other 
districts  of  the  Lake  Superior  region  is  the  production  in  some  way  of  a 
pitching  trough  which  is  relatively  impervious.  Where  the  jDitching, 
impervious  troughs  are  large  and  continuous,  as  at  the  Chapin,  Pewabic, 
and  Aragon  mines  (see  tigs.  30,  32,  34,  3.5,  40,  44,  46,  and  47),  the  ore 
deposits  are  almost  sure  to  be  large.  Where  the  pitching  troughs  are  small, 
irregular,  or  broken,  the  ore  deposits  are  likely  to  be  small. 

At  first  sight  the  firms  of  the  ore  deposits  might  be  thought  to  be 
exceedingly  irregular,  but  when  the  above  relations  are  understood  they 
appear  to  have  orderly  forms.  A  main  mass  of  ore  is  likely  to  be  at  the 
bottom  of  a  trough,  but  from  this  main  mass  a  considerable  belt  of  ore 
may  follow  along  the  limbs  of  the  trough  to  a  much  higher  altitude  than  in 
the  center  of  the  trough.  The  ore  bodies  in  cross  sections  thus  frequently 
constitute  a  U ,  which  is  very  thick  at  the  bottom,  the  center  of  the  U  beino- 
occupied  by  the  iron  formation  which  has  not  been  transformed  to  ore  (see 
plats  of  Aragon  mine,  figs.  39,  40).     If  the  fold  is  very  nnich  compressed, 


394  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  limbs  of  the  U  may  unite  at  the  center  and  produce  a  pitching  lens, 
with  its  lower  extremity  rounded  to  conform  with  the  shape  of  the  trough 
of  the  fold  and  its  upper  limit,  where  not  at  the  surface,  more  or  less 
irregular  in  shajie  in  consequence  of  the  gradual  passage  of  the  ore  into 
jaspilite.  The  Chapin  deposits  are  good  illustrations  of  such  lenses.  The 
deposits  formed  at  contacts  are  usually  much  more  irregular  than  those 
formed  in  troughs.  In  general,  they  are  broad  and  thin,  or  sheet-like 
masses  with  irregular  boundaries  on  all  sides.  Their  lower  surfaces  are 
the  most  even  and  the  best  defined,  but  even  these  are  undulatory.  For 
the  most  part  they  remain  near  the  contact  of  the  iron-bearing  formation 
with  the  underlying  one,  but  at  many  places  they  leave  this  contact, 
rise  into  the  iron-bearing  beds,  and  thus  become  separated  from  the  base 
of  the  formation  by  considerable  thicknesses  of  jaspilites.  The  upper  sur- 
faces are  much  more  uneven  than  the  lower  ones.  They  are  not  only 
undulatory  to  a  greater  degree,  but  ore  projections  extend  upward  into  the 
overlying  jaspilites,  and,  ramifying  through  these  in  an  extremely  irregular 
manner,  often  coalesce  and  inclose  lenses  of  jaspilite  and  then  continue  their 
separate  courses  until  the  contact  with  the  overlying  slates  is  reached, 
where  thev  again  coalesce,  spread  out,  and  form  a  second  sheet-like  expan- 
sion, which,  however,  is  usually  much  thinner  and  much  less  extensive  than 
the  deposit  at  the  lower  contact.  In  other  words,  the  shapes  of  tlie  contact 
deposits  correspond  to  the  shapes  of  channels  that  would  be  occupied  by 
percolating  water  descending  to  lower  levels  mainly  along  the  lower  contact 
plane,  but  also  through  any  openings  that  might  oifer  themselves  in  the 
course  of  its  downward  passage.  Where  openings  across  the  formation 
offered  easier  passages  than  that  along  the  contact  plane,  the  water,  or  some 
of  it,  naturally  utilized  these  and  followed  them  until  they  were  intersected 
by  other  openings  offering  a  channel  with  a  more  nearly  vertical  descent, 
when  it  left  the  former  channel  and  continued  its  course  in  the  latter  one. 
Since  the  upper  contact  of  the  formation  with  the  overlying  slates  is  apt  to 
offer  a  channel  similar  to  that  at  the  lower  contact,  we  find  that  here  also 
the  water  spread  out  and  deposited  sheet-like  masses  of  ore  like  that  at  the 
lower  level,  but  smaller.  Peposits  of  this  kind  occur  principally  in  the 
straight  portions  of  the  formation,  where  folding  is  absent  and  where  the  dip 
is  not  overturned.  A  portion  of  the  deposits  of  the  West  Vulcan  and  Verona 
mines  are  of  this  class  (see  figs.  46  and  51). 


ALGONKIAN,  THE  ORE  DEPOSITS.  395 


DEVELOPMENT   OF    THE    DEPOSITS. 


From  the  foregoing  statements  of  facts  concerning  the  distribution, 
methods  of  occurrence,  and  situations  of  the  ore  deposits,  it  must  be  evi- 
dent that  the  ores  of  the  Menominee  district,  hke  those  of  the  Gogebic  and 
Marquette  districts,  were  concentrated  by  waters  moving  along  in  definite, 
if  not  always  circumscribed,  channels.  Van  Hise,"  in  his  discussion  of  the 
principles  controlling  the  deposition  of  ores,  classified  ore  deposits  produced 
by  underground  waters  into  three  main  classes:  (1)  Ores  which  at  the  place 
of  precipitation  are  deposited  by  ascending  waters  alone;  (2)  ores  which  at 
the  place  of  precipitation  are  deposited  by  descending  waters  alone;  and  (3) 
ores  which  receive  a  first  concentration  by  ascending  waters  and  a  second 
concentration  by  descending  waters.  The  ores  of  the  Menominee  district, 
like  those  of  the  other  Lake  Superior  iron-ore  districts,  belong  to  the  second 
class.  The  principal  deposits  are  above  an  impervious  basement,  this 
impervious  basement  is  in  a  pitching  trough,  and  the  ore  formation  in  the 
pitching  trough  is  often  much  broken.  Smaller  deposits  occur  without 
pitching  troughs  at  contacts,  fault  planes,  and  at  sharp  folds,  where  the  iron 
formation  is  fractured. 

These  relations  of  the  oi'e  deposits  to  the  troughs  (see  sections  and 
plans  of  mines)  are  such  as  to  show  clearly  that  the  iron  ores  must  have 
been  deposited  in  their  present  position  after  the  troughs  were  formed. 
No  igneous  or  sedimentary  rock  as  originall}^  produced  has  such  forms  as 
those  exhibited  by  most  of  the  ore  bodies.  These  clearly  are  not  alto- 
gether original  sedimentary  rocks,  such  as  the  iron-bearing  formation  as 
a  whole  is,  but  they  grade  into  the  other  rocks  of  the  Vulcan  formation. 
The  ore  bodies  clearly  are  not  igneous  rocks.  No  igneous  rocks  ever 
grade  by  imperceptible  stages  into  sedimentary  rocks,  such  as  the  vari- 
ous members  of  the  iron-bearing  formation  are.  If  the  iron  ores  were 
deposited  in  their  present  position  after  the  troughs  were  formed,  as 
the  foregoing  facts  seem  to  show  beyond  question,  they  nmst  have  been 
produced  by  the  work  of  underground  circulating  waters.  Further, 
the  positions  of  the  principal  deposits  in  jiitching  troughs  bottomed  by 
impervious  basements  rather  than  in  pitching  arches  topped  b}^  impervious 
covers    are    conclusive    evidence    that    the    ores    were    concentrated    by 

"VanHise,  C.  R.,   Some  principles  controlling  the  deposition  of  ores:    Trans.   Am.   Inst.   Min. 
Eng.,  vol.  30,  1900,  pp.  178-174. 


396  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

descending  vather  than  by  ascending  water.  Descending  waters  would  be 
converged  by  iiitcliiug  troughs  with  impervious  basements,  whereas 
ascending  waters  would  be  converged  in  pitcliing  arches  having  impervious 
roofs.  In  this  connection  it  is  also  to  be  noted  that  the  ores  are  almost 
exclusively  hematite;  that  is,  they  belong  to  the  class  of  oxidized  ores.  The 
products  therefore  accumulated  under  conditions  favorable  to  oxidation  and, 
if  secondary  concentrates,  they  must  have  been  precipitated  by  water  bearing 
oxygen.  Such  waters  are  usually  descending,  hence  the  character  of  the 
deposits  makes  it  probable  that  the  waters  producing  the  ores  were 
descending  rather  than  ascending.  The  nature  of  the  minerals  associated 
with  the  ores  is  also  corroborative  evidence  tliat  the  deposits  were  made 
by  circulating  water,  and  the  fact  that  these  associated  minerals  are 
apparently  more  abundant  in  the  lower  portions  of  the  deposits  than  in 
the  upper  portions  (p.  389)  might  be  urged  as  indicating  that  the  waters 
were  descending,  or  at  any  rate  that  the  ore  deposits  lie  in  the  courses  of 
waters  descending  at  the  present  time.  Since  there  has  been  no  appreciable 
deformation  of  the  district  since  the  deposits  were  formed,  it  is  probable 
that  the  circulation  of  earlier  times  followed  the  same  courses  as  the 
present  circulation. 

That  the  ores  of  the  Menominee  district  were  concentrated  and 
enriched  by  descending  waters  seems  to  be  proved  beyond  question.  From 
the  nature  of  the  ores  and  the  character  of  their  environment  it  is  prac- 
tically certain  that  the  Menominee  deposits  were  prodiaced  in  the  same 
manner  and  by  the  same  processes  as  those  of  the  Gogebic,  the  Mesabi,  and 
the  Marquette  districts.  But  in  the  Menominee  district  the  folding  has  been 
so  close  and  the  protection  afforded  to  the  original  material  which  gave  rise 
to  the  ores  has  been  so  scanty"  that  these  processes  have  been  carried  to 
completion,  so  far  as  the  surface  and  the  depths  open  to  our  inspection  are 
concerned,  and  the  steps  along  which  they  have  proceeded  have  been  so 
thoroughlj^  obliterated  that  they  can  not  be  followed  with  the  same  certainty 
as  in  tlie  other  three  districts  mentioned.  The  process  of  concentration  has 
been  so  fully  discussed  by  Van  Hise*  in  the  reports  on  the  Grogebic  and 

"Compare  Van  Hise,  C.  R.,  and  Bayley,  W.  S.  (with  H.  L.  Smyth),  The  Marquette  iron-bearing 
district  of  Michigan:  Mon.  U.  S.  Oeol.  Survey,  vol.  28,  1897,  p.  381. 

''Irving,  R.  D.,  and  Van  Hise,  C.  R.,  The  Penoljee  iron-bearing  series  of  Michigan  and  Wisconsin: 
Mon.  U.  S.  Geol.  Survey,  vol.  19,  1892,  pp.  .534.  Van  Hise,  C.  R.,  and  Bayley,  W.  S.  (with  H.  L. 
Smyth),  The  Marquette  iron-bearing  district  of  Michigan:  Mon.  U.  S.  Geol.  Survey,  vol.  28,  1897, 
pp.  608.     With  atlas  of  39  plates. 


ALGONKIAN.  THE  ORE  DEPOSITS.  397 

the  Marquette  districts,  and  by  Leith"  in  the  report  on  the  Mesabi  district, 
that  little  can  be  added  to  the  explanations  there  given.  These  explanations 
apply  as  well  to  the  Menominee  district  as  to  the  other  iron-ore  districts  of 
the  Lake  Superior  region,  and  therefore  they  are  drawn  upon  freely  in  the 
following  pages. 

The  greatest  apparent  difference  lietween  the  deposits  of  the  Menominee 
and  the  other  districts  is  the  comparatively  large  quantity  of  clastic  ore 
in  the  former.  In  addition  to  this  fragmental  ore,  ;v  large  portion  of  the 
iron  of  the  ore  bodies  in  the  Menominee  district  was  deposited. in  its 
present  position  as  an  original  sediment,  containing  silica  and  other  impuri- 
ties, which  has  since  been  chemically  changed;  that  is  to  say,  some  of  it 
was  deposited  as  iron  carbonate  or  as  greenalite,  and  later  transformed  to 
iron  oxide  in  situ.  Another  part  is  iron  oxide  secondarily  deposited,  by 
whicli  the  originally  lean  material  has  been  enriched,  forming  an  ore  body. 
The  process  of  enrichment  involved  concentration  of  the  iron  from  a  source 
capable  of  yielding  it,  convergence  of  solutions  can-ying  it  into  trunk 
channels,  and  conditions  favorable  to  its  chemical  precipitation.  The 
source  of  the  iron  for  the  enrichment  of  the  ores  is  believed  to  have  been 
partly  iron  carbonate  and  partly  greenalite.  In  spite  of  the  fact  that  the 
iron-bearing  members  of  the  Vulcan  formation  are  largely  fragmental  and 
contain  no  residual  iron  carbonate  or  greenalite,  it  is  probable  that  origi- 
nall}^  mingled  with  their  material  were  large  quantities  of  these  compounds. 
The  jaspilites,  which  constitute  a  considerable  portion  of  the  formation, 
have  elsewhere  in  the  Lake  Superior  region  been  genetically  connected 
with  iron-bearing  carbonates  and  silicates,  and  there  is  every  reason  for 
believing  that  they  have  had  a  similar  origin  in  the  Menominee  district. 
The  ferriferous  compounds  within  the  Vulcan  formation  were  originally, 
therefore,  probably  somewhat  abundant.  If  this  is  so,  the  concentration 
of  the  ores  at  the  particular  places  where  they  now  occur  may  be  fully 
explained.  However,  we  are  not  restricted  to  the  iron  compounds  of  this 
formation  as  a  source  of  the  iron  for  the  solutions.  Tlie  Hanbury  slate 
still  contains  a  considerable  amount  of  iron  carbonate,  from  which  there 
have  been  developed  within  the  slates  small  bodies  of  chert,  jasper,  and 
iron  ore  (see  p.  480).  While  no  workable  ore  deposits  have  been  found  in 
the  Hanbury  slate  in  this  district  the  siderite  there  present  may  have 
played  an  important  role  in  the  production  of  the  iron-ore  deposits  in  the 

"Op.  cit.,  p.  316. 


398  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Vulcan  formation.  These  iron  carbonates  are  more  abundant  at  low  hori- 
zons than  at  liig-h  horizons;  that  is,  are  more  plentiful  adjacent  to  the 
Vulcan  formation.  •  The  foregoing  facts  render  it  highly  jn'obable  that 
percolating  waters  within  the  Hanbury  formation  took  ujo  iron  carbonate, 
passed  down  into  the  Vulcan  formation,  and  contributed  iron-bearing  solu- 
tions for  the  enrichment  of  the  oi'e  bodies. 

The  chemical  reactions  which  resulted  in  the  concentration  and 
enrichment  of  the  ores  depend  upon  the  mingling  of  waters  containing 
oxygen  with  those  containing  iron  carbonate."  The  waters  following 
circuitous  routes,  and  especially  those  passing  through  the  Hanbur}-  slate, 
had  their  oxygen  abstracted  by  the  iron  carbonate  in  an  early  stage  of 
their  journey.  In  this  way  the  limonite  and  hematite  of  the  Hanbury 
slate  developed  (see  p.  476  et  seq.). 

In  the  process  of  precipitation  of  these  oxides  carbon  dioxide  was 
liberated  and  dissolved  in  the  descending  waters.  Thus  carbonated  waters 
freer  from  oxygen  were  produced,  and  these  took  up  in  solution  more  iron 
carbonate.  Large  quantities  of  these  solutions  were  converged  upon  the 
sides  or  at  the  bottom  of  the  pitching  troughs,  or  in  other  places  where 
there  were  trunk  channels  foi'  water  circulation.  Water  more  directly  from 
the  surface,  and  especially  that  passing  only  through  the  Vulcan  formation, 
which  coiitained  little  iron  carbonate,  at  least  in  the  later  stages  of  the 
process,  retained  its  oxygen.  The  waters  bearing  iron  carbonate  and 
oxygen  were  thus  commingled.  The  result  was  the  precipitation  of  iron 
sesquioxide.  Furthermore,  the  great  quantity  of  downward-moving  water, 
converged  into  the  troughs,  took  silica  into  solution  and  transported  it 
elsewhere,  and  thus  ab.stracted  this  deleterious  element,  its  place  being 
taken  by  the  deposited  iron  oxide. 

It  has  been  seen  that  the  waters  which  can-ied  iron  carbonate  to  the 
ore  deposits  were  carbonated.  The  ))recipitation  of  iron  oxide  from 
carbonate  liberated  more  carbon  dioxide,  so  that  the  waters  were  very 
heavily  charged  with  carbonic  acid,  and  consequently  were  particularly 
efficient  solvents  for  the  iron  carbonate. 

The  iron  oxide  of  an  ore  body  thus  consists  in  part  of  iron  compounds 
originally  deposited  in  situ  and  in  part  of  iron  brought  in  by  underground 
waters.  Which  of  the  two  constituents  of  the  iron  ore,  the  original 
material  or  that  added  by  underground  water,  is  on  the  average  more 

aCf.  Mon.  U.  S.  Geol.  Survey,  vol.  43,  1903,  pp.  260-265. 


ALGONKIAN,  THE  ORE  DEPOSITS.  399 

abundant  it  is  impossible  to  say.  It  is  almost  certain  that  in  some  cases 
the  original  detrital  iron  oxide  is  the  more  abundant,  and  in  t)ther  cases 
that  the  material  added  by  underground  water  is  more  abundant ;  but  in 
all  cases  it  may  be  said  that  were  it  not  for  the  secondary  enrichment  by 
underground  waters  through  the  addition  of  iron  oxide  and  the  abstraction 
of  silica  the  material  would  not  be  iron  ore.  The  evidence  of  this  lies  in 
the  fact  that  the  ore  bodies  are  universally  confined  to  the  places  where 
underground  waters  have  been  converged  into  trunk  channels.  In  order 
that  this  process  should  have  produced  the  large  ore  bodies,  it  is  necessary 
that  it  should  have  continued  for  a  long  period  during  progressive  denuda- 
tion. Many  of  the  large  ore  bodies  known  in  the  district  somewhere  reach 
the  surface.  The  secondary  material  now  found  near  the  surface  must 
have  been  derived  largely  from  the  upper  portions  of  the  Vulcan  formation 
and  from  the  Hanbury  formation,  i.  e.,  from  material  which  was  once  at 
higher  levels,  but  which  since  has  been  removed  by  erosion. 

During  tlie  process  of  denudation  the  ore  deposits  must  have  begun 
to  be  formed  shortly  after  the  iron-bearing  formation  was  ctit  through. 
For  a  time  they  increased  in  size,  but  it  is  probable  that  later  the  increase 
in  size  practically  ceased,  for  when  the  oxidizing  waters  reached  the  limit 
of  their  working  depth  denudation  must  have  removed  the  ores  at  the 
top  as  rapidly  as  they  were  formed  beneath.  However,  with  lowering  of 
the  upper  surface  there  was  a  corresponding  lowering  of  the  inferior  limit 
at  which  the  waters  worked,  and  a  consequent  continuous  migration  of  the 
deposit  downward  pari  passu  with  denudation.  On  account  of  the  pitch 
of  the  basements  in  which  the  deposits  were  formed,  lateral  migration  must 
have  accompanied  downward  migration.  We  therefore  must  conceive  of 
the  iron-ore  deposits  as  slowly  migrating  downward  through  thousands  of 
feet,  their  lower  surfaces  at  any  given  time  being  just  in  advance  of  the  plane 
of  erosion.  As  denudation  proceeded  a  part  of  the  ores  must  have  been  car- 
ried away  mechanically  and  thus  lost.  Another,  but  probably  a  relatively 
small  part,  was  doubtless  taken  into  solution  and  carried  downward,  to  be 
precipitated  again  at  lower  levels.  However,  as  erosion  extended  down- 
ward and  swept  away  the  ore  at  the  surface,  the  process  of  concentration 
also  continued  downward,  so  that  the  amount  of  ore  existing  at  any  one 
period  through  much  of  the  pre-Glacial  tiuie  was  roughly  constant, 
although  there  was  doubtless  considerable  variation  in  its  quantity  de})end- 
ing  upon  topographic  and  climatic  conditions  during  the  different  periods. 


400  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

For  that  portion  of  an  ore  deposit  which  now  reaches  the  surface  or  is 
overlain  by  completely  altered  cherts,  it  is  probable  that  there  is  little  addi- 
tion in  iron  oxide  at  tlie  present  time;  for  it  has  already  been  explained  that 
the  iron  oxide  for  an  ore  deposit  is  mainly  derived  from  that  part  of  the  iron- 
bearing  formation  which  has  been  removed  by  erosion.  However,  it  does  not 
follow  that  the  enrichment  of  an  ore  deposit  by  the  abstraction  of  silica  has 
not  effectively  continued  after  practically  all  of  the  iron  was  added.  Indeed, 
there  is  every  reason  to  believe  that  the  solution  of  silica  has  continued  to 
the  present  time,  and,  moreover,  this  process  has  probably  been  more  effect- 
ive in  those  parts  of  an  ore  deposit  near  the  surface;  for  there  the  waters 
have  been  longest  at  work  in  abstracting  the  silica.  It  is  a  well-known  fact 
that  in  many  mines  there  is  a  tendency  for  the  silica  to  run  somewhat  lower 
in  the  upper  than  in  the  lower  levels  of  the  deposits,  and  this  is  readily 
explained  by  the  greater  depletion  of  silica  in  the  upper  than  in  the  lower 
parts  of  deposits.  Also  many  of  the  ore  deposits  have  a  broken  and  porous 
character,  and  appear  to  have  sagged,  as  if  some  compound  or  compounds 
had  been  abstracted.  The  material  abstracted  was  doubtless  mainly  silica. 
Moreover,  as  has  been  indicated  in  a  preceding  page  (p.  389),  silicates  appear 
in  some  cases  to  have  been  leached  from  the  upper  jjortions  of  the  deposits, 
if  not  also  deposited  in  lower  j^ortions.  It  is  probable  that  some  of  the 
porosity  referred  to  above  is  due  to  the  abstraction  of  serpentine  and 
talc,  although  the  cavities  which  these  substances  occupied  may  have  been 
formed  originally  by  the  removal  of  silica  The  tendency  of  the  abstrac- 
tion of  these  two  minerals  would  be  to  diminish  the  contents  of  magn,esia, 
silica,  and  water  in  the  ore,  and,  as  a  consequence  of  this  diminution,  to 
increase  the  percentage  of  iron. 

Furthermore,  the  ore  deposits  seem  to  have  been  made  more  valuable 
by  the  abstraction  of  pliosphorus  and  sulphur  compounds  by  descending 
waters  in  a  way  similar  to  the  abstraction  of  silica  and  silicates.  The  most 
notable  published  cases  illustrating  this  process  are  those  of  the  Ludingion 
mines,  described  by  Browne  (see  p.  89),  and  of  the  Pewabic  and  Aragon 
mines,  described  by  Brown"  and  Larssou,*"  where  the  deposits  near  the 
surface  are  low  phosphorus  and  those  deeper  down  are  high  phosphorus  ores. 
In  general  the  phosphorus  seems  to  be  low  where  the  iron  is  high  and  the  ore 

"Brown,  E.  F.,  Distribution  of  phosphorus  and  system  of  sampling  at  the  Pewabic  mine:   Proc. 
Lake  Superior  Min.  Inst.,  vol.  3,  1895,  p,  49. 
*Larsson,  Per,  ibid.,  p.  55. 


ALGONKIAN,  THE  ORE  DEPOSITS.  401 

porous,  and  therefore  where  the  water  circulation  was  very  effective.  The 
same  is  true  of  sulphur,  but  to  a  much  less  noticeable  extent,  because  of 
the  very  slight  quantity  of  this  element  in  the  ores  of  the  district.  The 
formation  of  sodium  sulphate  as  an  efflorescence  on  the  ores  exposed  in 
stock  piles  indicates  that  the  sulphur  is  oxidized  under  the  influence  of 
meteoric  waters  and  forms  a  soluble  salt,  which  naturally  must  be  carried 
off  by  moving  water.  The  oxidizing  waters  that  gain  access  to  the  ore 
deposits  should  produce  similar  effects,  and,  as  a  consequence,  the  ore 
should  be  rendered  more  valuable  thereby.  It  is  a  well-substantiated  fact 
that  iron  ores  which  have  been  exposed  to  the  atmospheric  agencies  for  a 
considerable  lapse  of  time  lose  both  phosphorus  and  sulphur. 

In  conclusion  we  may  therefore  say  that  the  chemical  processes  have 
tended  to  make  the  ore  deposits  more  valuable  at  the  present  time,  although 
the  additions  of  iron  may  have  long  since  ceased. 

TOPOGRAPHIC    RELATIONS   OF   THE    DEPOSITS. 

In  order  to  produce  great  masses  of  ore,  such  as  some  of  those  charac- 
terizing the  Menominee  district,  the  water  circulation  must  have  been  long 
continued.  The  volume  of  water  which  circulated  through  the  ore  deposits 
must  have  been  many  thousand  times,  probably  hundreds  of  thousands  of 
times,  as  great  as  the  volume  of  ore.  It  is  certain  that  as  depth  increases 
the  rocks  in  the  earth's  crust  become  more  and  more  compact,  until  finally 
the  zone  of  rock  flowage  is  reached,  into  which  the  water  can  not  be  assumed 
to  pass.  We  therefore  must  conclude  that  water  converged  into  trunk 
channels  must  again  reach  the  surface.  Hence  we  find  that  the  majority 
of  the  ore  deposits  where  they  approach  the  surface  are  on  the  slopes  of  the 
elevations,  the  crests  being  usually  occupied  by  the  Randville  dolomite  or 
the  Cambrian  sandstone.  This  is  true  for  all  of  the  important  mines  of  the 
district  with  the  exception  of  the  Chapin,  the  Aragon,  and  the  Loretto. 
However,  each  of  these  deposits  is  so  connected  with  troughs  which  rise 
toward  the  higher  grounds  as  to  make  it  almost  certain  that  they  had  elevated 
feeding  areas.  Moreover,  while  the  Chapin  deposit  was  discovered  in  low- 
lying  ground,  a  little  way  to  the  west  is  the  broad  valley  of  the  Menominee 
River,  which  is  still  lower.  Probably,  therefore,  there  were  lower  areas 
where  the  water  issued.  However,  it  is  possible  that  in  the  subordinate 
cross  valley  at  the  Chapin  mine  descending  oxidizing  waters  met  ascending- 
carbonate-bearing  waters,  and  thus  precipitated  a  part  of  this  deposit. 

MON    XLVI — O-t 26 


402  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

The  crests  of  the  elevations  above  the  Ludingion,  Millie,  Walpole,  and 
Pewabic  mines  rise  to  1,500  or  1,600  feet  above  sea  level.  The  broad 
valley  of  the  Menominee  to  the  west  has  an  elevation  of  about  1,060  feet, 
and  this  valley  is  probably  filled  to  the  depth  of  100  feet  or  more.  Between 
Prospect  Hill  and  Hughitt  Bluff  is  a  subordinate  cross  valley.  In  this  valley 
is  the  Chapin  mine,  the  surface  of  which  has  an  elevation  of  only  about 
1,150  feet,  or  not  more  than  90  feet  above  the  valley  of  the  Menominee 
River;  but  if  the  valley  of  the  river  is  filled  to  a  depth  of  100  feet  by  sand 
and  gravel  the  elevation  of  the  present  surface  at  the  Chapin  mine  is  190 
feet  above  the  rock  floor  under  the  river  channel. 

With  respect  to  the  other  mines  of  the  district  the  relation  between  the 
topography  and  the  ore  deposits  is  in  strict  accord  with  the  theory  that 
the  ores  are  the  result  of  the  action  of  descending  waters;  although  in  this 
district  this  relation  does  not  corroborate  the  theory  as  effectually  as  it 
does  in  some  of  the  other  districts.  While  it  is  true  that  nearly  all  the 
ore  deposits  of  the  Menominee  district  thus  far  discovered  are  on  hillsides, 
nevertheless  it  is  also  true  that  the  iron  formation  is  nowhere  at  low  levels 
except  in  the  vicinity  of  the  Chapin,  Aragon,  and  Loretto  mines,  as  before 
mentioned.  The  great  dolomite  constitutes  the  dominant  factor  in  deter- 
mining the  positions  of  the  elevations.  The  iron  formation  lies  immediately 
upou  this,  and  consequently  must  of  necessity  be  on  the  slopes  of  hills, 
and,  since  the  ore  deposits  are  in  this  formation,  these,  too,  must  be  on  hill 
slopes.  The  principal  value  of  the  discussion  of  the  relation  between  the 
topography  of  the  Menominee  district  and  its  ore  deposits  is  to  show  that 
this  district  offers  no  im])ortant  exceptions  to  the  generalization  that  the 
iron- ore  deposits  of  the  Lake  Superior  region  are  usually  situated  below 
slopes  or  crests. 

East  of  Iron  Mountain  it  is  notable  that  adjacent  to  each  of  the  locali- 
ties where  important  mines  are  found  there  are  valleys  across  the  south 
limestone  i-ange  and  the  Vulcan  formation,  although  these  valleys  are  now 
partly  filled  with  thick  deposits  of  drift.  East  of  the  Quinnesec  mine  is 
the  low-lying  area  now  partly  occupied  by  the  road  running  north.  North- 
east of  Norway  is  another  transverse  depression.  The  Norway  mine  is 
located  on  the  hill  to  the  northwest.  The  West  Vulcan  mine  is  located  on 
Brier  Hill,  to  the  northeast.  The  Aragon  mine  is  in  the  depression.  East 
of  the  East  Vulcan  and  Verona  mines  is  the  valley  of  the  Sturgeon  River. 


ALGONKIAN,  THE  ORE  DEPOSITS.  403 

The  Breeii  mine  is  on  a  slope  with  a  cross  valley  immediately  to  the  west. 
The  Loretto  mine  pitches  directly  below  the  valley  of  the  Sturgeon  River. 
Adjacent  to  the  central  range  of  dolomite  the  most  important  deposit  is  the 
Traders.  This  mine  is  on  the  westward  slope  of  a  hill  which  rises  to  an 
elevation  of  1,500  feet.  The  ore  deposit  pitches  toward  the  valley  of  the 
Menominee  only  a  short  distance  to  the  west. 

Thus  it  appears  that  nearly  all  of  the  large  ore  deposits  in  the 
Menominee  district  are  either  related  to  the  topography  in  the  same 
manner  as  ai'e  the  deposits  in  the  other  Lake  Superior  iron-ore  producing 
'  districts,  or  that  their  relations  are  such  as  can  be  explained  on  the 
supposition  that  before  the  district  was  denuded  hj  erosion  agencies  they 
were  surrounded  by  elevations  greater  than  those  at  which  the  surfaces  of 
the  deposits  then  lay. 

TIME   AND    DEPTH    OF   CONCENTBATION. 

The  beginning  of  the  tinal  concentration  of  the  Menominee  ores  must 
have  been  after  the  folding  which  produced  the  troughs  and  after  the 
removal  of  the  Hanbury  formation  covering  the  Vulcan  formation — that  is, 
in  the  interval  between  the  Upper  Huronian  and  the  Upper  Cambrian.  In 
this  district  it  is  certain  that  the  process  of  concentration  was  carried  far 
toward  completion  before  the  end  of  Cambrian  time,  for  considerable  areas 
of  the  Huronian  rocks  and  certain  of  the  ore  bodies  themselves,  as,  for 
instance,  parts  of  those  of  the  Traders,  Cuff,  Chapin,  Pewabic,  Walpole, 
Quinnesec,  Norway,  Cyclops,  Breen,  Emmett,  and  other  mines,  are  capped 
by  the  Upper  Cambrian  sandstone,  at  the  base  of  which  are  detrital  ores 
derived  from  the  ore  deposits  below  during  the  Cambrian  transgression 
over  the  area.  It  is  therefore  highly  probable  that  the  main  concentration 
of  the  iron  ore  of  the  deposits  of  the  Menominee  district  took  place  before  the 
end  of  the  Cambrian  period,  although  since  that  time  there  probably  has 
been  additional  enrichment,  mainly  by  the  solution  of  silica,  magnesia, 
phosphorus,  and  sulphur,  and  the  deposition  of  some  iron  oxide.'' 

o  A  large  portion  of  the  above  discussion  of  the  development  of  the  ores  and  their  relations  to  the 
topography,  as  well  as  the  statement  as  to  the  time  and  depth  of  concentration,  is  taken  almost 
verbatim  from  Van  Hise's  paper  on  the  iron-ore  deposits  of  Lake  Superior,  "The  iron-ore  depo-sits 
of  the  Lake  Superior  region:"  Twenty-first  Ann.  Kept.  U.  S.  Geol.  Survev,  pt.  3,  1901,  pp.  323-332, 
396^00. 


404  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

ILLUSTRATIONS   OF   DEPOSITS,    INCLUDING    GEOLOGY   OF  THE    IMPORTANT  MINES. 

The  ore  deposits  now  being  exploited  and  those  that  have  been  worked 
in  the  past  are  confined  to  three  belts: 

(1)  The  Loretto-Appleton  belt,  east  of  the  locality  where  the  northern 
and  sonthern  belts  of  dolomite  unite,  or,  at  least,  where  they  approach  very 
near  to  one  another. 

(2)  The  Traders,  Cuff,  Cornell,  Indiana,  and  Forest  belt,  mainly  south 
and  west  of  the  central  dolomite  belt,  and  possibly  also  in  one  case  north 
of  it. 

(3)  The  belt  extending  from  the  Menominee  River  on  the  west  to 
Waucedah  on  the  east,  lying  on  the  south  flank  of  the  sonthern  belt  of 
dolomite.  On  this  belt  are  situated  the  Ludington,  Chapin,  Walpole, 
Pewabic,  Keel  Ridge,  Vivian,  Quinnesec,  Cundy,  Norway,  Perkins,  Cyclops, 
Aragon,  Brier  Hill,  Cuny,  West  Vulcan,  Central  Vulcan,  East  Vulcan, 
Verona,,  Breen,  and  Emmett  mines,  besides  many  as  yet  unnamed  explora- 
tions to  the  west  of  Iron  Mountain. 

LORETTO-APPLETOS  DEPOSIT. 

The  Loretto-Appleton  deposit,  more  particularly  that  portion  being 
exploited  by  the  Loretto  mine,  furnishes  one  of  the  most  typically  devel- 
oped trough  deposits  to  be  found  in  the  district.  West  of  the  Loretto  mine 
the  northern  and  central  belts  of  dolomite  probably  join  (see  maps.  Pis.  IX 
and  XXIII),  giving  continuous  dolomite  from  the  Sturgeon  quartzite  on  the 
north  to  the  southern  iron-bearing  belt  on  the  south,  or,  at  any  rate,  if  not 
at  the  surface,  the  dolomite  bridges  this  interval  a  short  distance  beneath 
the  surface,  the  surface  rocks  in  this  case  being  a  thin  layer  of  the  lower- 
most beds  of  the  Traders  member  of  the  Vulcan  formation.  East  of  this 
bridge  of  dolomite,  between  the  northern  and  southern  belts  of  dolomite, 
is  the  iron-bearing  Vulcan  formation.  To  the  west  of  the  bridge  are  possibly 
the  iron-bearing  Vulcan  formation  and  certainly  the  Hanbury  slates.  It  is 
therefore  clear  that  a  cross  anticline  here  exists  which  brings  to  or  near  the 
surface  the  dolomite  that  to  the  east  and  west  is  buried  beneath  the  younger 
rocks.  Hence  it  follows  that  the  major  structure  adjacent  to  the  Loretto  mine 
is  that  of  an  eastward-plunging  syncline,  the  dolomite  being  to  the  north,  to 
the  south,  and  to  the  west.  From  an  inspection  of  the  surface  map  of  the 
mines  it  will  be  seen  that  this  syncline  is  widest  to  the  west  and  is  here 


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ALGONKIAN,  THE  ORE  DEPOSITS. 


405 


composed  of  a  northern  subordinate  syncline,  separated  from  a  southern 
monocline  (see  cross  section,  fig.  30)  l)y  a  narrow,  compressed  anticline. 
These  folds  pass  to  the  east  into  what  appears  to  be  a  simple  syncline,  which 
continues  at  least  as  far  as  the  Appleton  mine.  The  rocks  involved  in  the 
folds  are  the  Randville  dolomite,  the  Traders  quartzites  and  jaspilites,  and 


,  ','firift ; 


Fig.  30.— Vertical  north-south  cross  section  of  the  Loretto  mine.     (Section  A-A  in  fig.  31.) 

the  Brier  slates.  The  dolomite  nowhere  reaches  the  surface,  but  it  is  found 
in  drill  holes  under  the  jaspilites  at  several  points.  The  Brier  slates  occur 
in  tlu'ee  small  areas,  capping  the  jaspilites  along  the  axis  of  the  syncline. 
Thus  in  longitudinal  section  there  are  three  synclines  and  two  anticlines 
from  the  west  side  of  the  Loretto  mine  to  the 

east  side  of  the  Appleton  property.  |u= 

The  principal  surface  rocks  within  the 
boundaries  of  the  syncline  are  the  Traders 
jaspilites.  These  are  bounded  on  the  north 
by  the  Traders  quartzites,  and  the  same  rocks 
may  occur  at  the  surface  at  the  crest  of  the 
first  anticline  west  of  the  Loretto  mine.     No 


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^^^1 


A 


exposures    of   the    quartzite    are    to    be    found    fig.  ai.-Horizontal  section  of  the  Loretto  mine 
T  1       ,    ,1  ,  1  •  ^    1        T  at  the  first  level.    Scale:  1  inch=250  feet. 

here,  but  the  eastern  workings  oi  the  Loretto 

mine  show  that  it  approaches  vei-y  close  to  the  surface,  and  that  a  short 
distance  farther  east  it  may  actually  reach  the  surface.  The  structure  of 
the  area,  if  the  inferences  above  outlined  are  correct,  is  that  of  an  east-west 
fairly  compressed  syncline  to  the  north,  jiassing  into  an  anticline  to  the 
south,  and  followed  farther  south  by  another  syncline,  the  south  portion  of 
which  has  not  been  seen.  These  folds  are  moreover  aff'ected  by  three  cross 
(north-south)  synclines,  separated  by  two  anticlines,  all  of  which  are  open. 
The  character  of  the  fold  in  wliich  the  main  Loretto  deposit  occurs  is 
beautifully  shown  by  the  horizontal  outline  of  the  ore  body  (see  fig.  31). 
The  outer  limit  of  the  ore  makes  a  broad  U  which  opens  to  the  east;  the 


406 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 


bottom  of  the  U  being  to  tlie  west.  The  cross  section  of  the  main  ore 
deposit  also  makes  a  wide  U ,  the  southern  hmb  of  which  passes  into  a  sharp 
subordinate  anticline  (fig.  30).  In  the  center  of  the  syncline  slate  caps  the 
ore.  Moreover,  the  longitudinal  section  of  the  mine  is  also  a  syncline 
(fig.  32)  likewise  capped  b)-  the  slate.  East  of  the  slate  capping  is  lean  ore- 
bearing  material,  which  passes  into  ore  under  the  slate  and  under  the  drift 
west  of  the  slate.  The  failure  of  the  rock  to  change  to  ore  east  of  the  slate  is 
apparently  due  to  the  cross  anticline,  which  has  prevented  the  convergence 
of  downward-moving  currents  of  water,  and  therefore  the  transformation  of 
the  rock  into  ore.  No  better  illustration  of  an  ore  body  in  a  trough  on  an 
impervious  basement  could  be  desired  than  that  furnished  by  this  deposit. 


West 


=•    ^^^   o      o    o 


East 

~3' 


,~°  c'^°"o°^'-'5       o     =>    o 


300  feet 


Tig.  32.— Vertical  east-west  longitudinal  section  of  the  Loretto  mine.     (Section  B-B  in  fig.  31.) 

The  southernmost  deposit  of  the  Loretto  mine  and  the  deposit  in  the 
Appleton  mine  had  not  been  suificiently  developed  to  warrant  statements 
as  to  their  relations  to  folds.  If  the  slate  south  of  the  south  deposit  of  the 
Loretto  mine  is  Brier,  as  is  supposed,  this  deposit  may  be  a  contact  deposit 
at  a  little  greater  depth  than  has  yet  been  reached.  The  slate  dips  slightly 
to  the  north  at  its  contact  with  the  iron-bearing  beds,  producing  a  steep 
slope  dipping  toward  the  ore  body,  which  slope  must  have  served  to  some 
extent  at  least  to  direct  descending  water  in  this  direction.  At  the  Appleton 
mine  the  greater  portion  of  the  ore  that  has  been  taken  out  (12,102  tons 
between  1892  and  1895)  was  obtained  from  north  of  the  shaft  on  or  near 
the  contact  of  the  jaspilites  with  the  underlying  Traders  slates. 


ALGONKIAN,  THE  ORE  DEPOSITS.  407 

TRADERS-FOREST  BELT. 

The  second  belt  of  the  Vulcan  formation,  that  adjacent  to  the  central 
belt  of  dolomite,  is  now  being  worked  only  at  the  Traders  and  the  Forest 
mines  at  the  two  extremities  of  the  belt.  Formerly  the  Cornell,  the  Cuff, 
and  the  Indiana  mines  were  also  in  operation.  The  Cornell  mine  ceased 
shipment  in  1887,  having  mined  49,302  tons  of  ore,  and  the  Indiana  ceased 
work  in  1886,  having  raised  17,871  tons.  The  Cuff  shipped  20,210  tons  in 
1899.  At  the  Forest  mine  exploration  has  not  proceeded  far  enough  to 
warrant  a  definite  statement  as  to  the  character  of  the  deposit. 

TRADERS    MINE. 

The  Traders  mine  is  at  the  west  end  of  the  Traders-Forest  ore-bearing 
belt,  which  in  this  vicinity  constitutes  a  westward-plunging  anticlinorium 
On  the  mine  property  are  two  pits — a  northern  one,  known  as  the  Traders 
pit,  and  a  southern  one,  known  as  the  Clifford  pit  (see  map,  PI.  XXIV). 
Southeast  of  the  Clifford  pit  and  distant  about  800  feet  is  the  abandoned 
pit  of  the  old  Cornell  mine.  The  formation  exposed  in  both  of  the  Traders 
pits  is  the  same  in  character.  It  consists  of  a  sheared  jasper  and  ore  breccia 
overlain  by  a  red  slate  and  underlain  at  the  Clifford  pit  by  a  ferruginous 
slate.  At  the  Traders  pit  the  ore  formation  strikes  nearly  north  and  dips 
at  55°  to  60°  to  the  west.  The  rock  is  jointed  and  schistose.  On  the  west 
side  of  the  pit  schistosity  and  bedding  are  approximately  parallel,  but  on 
the  east  side  the  strike  of  the  schistosity  varies  from  N.  10°  W.  to  N.  25° 
W.,  and  its  dip  from  50°  W.  to  80°  NE.  The  jointing  is  inclined  to  the 
schistosity  and  also  to  the  bedding.  At  the  northwest  corner  of  the  pit 
the  joints  strike  N.  30°  W.  and  dip  75°  W.  At  the  southeast  corner 
their  strike  is  N.  45°  W.  and  their  dip  25°  NE.  Where  the  schistosity 
and  jointing  are  inclined  to  the  bedding  the  latter  feature  is  exceedingly 
obscure.  The  variation  in  the  directions  of  the  schistosity  and  of  the 
joints  is  evidence  that  folds  of  some  kind  exist  here,  though  they  have  not 
been  detected,  and  these  may  be  connected  in  some  way  with  the  occur- 
rence of  the  ore. .  No  shipments  are  now  being  made  from  this  pit,  nor 
is  any  development  work  being  done.  The  ore  deposit  is  therefore  not 
thought  to  be  promising  under  the  present  conditions  of  the  ore  market. 
The  contact  of  ore  beds  with  the  overlying  Brier  slates  is  plaiidy  seen  on 
the  walls  of  the  pit  at  the  southwest  corner.  Beyond  this  to  the  west  are 
two  pits  in  red  slates,  and  about  200  feet  farther  west  is   a  third   pit  in 


408  THE  MENOMI^"EE  IRON-BEARING  DISTRICT. 

jaspilites  that  may  belong  in  the  Cuiry  member.  Northwest  of  the  pit  is 
an  old  shaft,  on  the  dump  of  which  are  fragments  of  red  sandstone  and  of 
gray  sheared  quartzite.  It  is  probable  that  this  is  a  quartzose  bed  in  the 
Hanbury  formation;  but  since  quartzites  are  found  also  in  the  Traders 
formation,  not  much  confidence  can  be  placed  in  this  identification.  If  the 
rock  is  a  component  of  the  Hanbury  formation,  the  Traders  beds  must 
swing  to  the  east. 

Northeast  of  the  Traders  pit,  at  what  is  known  as  the  Juno  explora- 
tion, are  two  shafts  that  offer  another  problem.  Here  the  rocks  on  the 
dumps  are  sandstone  and  an  abundance  of  an  evenly  banded  jaspilite 
quite  unlike  the  brecciated  rock  of  the  Traders  and  Clifford  pits.  Some  of 
the  jasper  is  of  the  flinty  or  waxy  kind,  characteristic  of  the  typical 
jaspers.  In  other  specimens,  however,  the  siliceous  component  is  a  gray 
quartzite  or  chert  that  resembles  very  closely  some  of  the  cherty  phases  of 
the  Curry  jasper.  Two  suggestions  offer  themselves  in  explanation  of  this 
occurrence — (1)  the  jaspilites  may  belong  in  the  Curry  member  on  the  east 
side  of  an  anticline  and  across  its  crest  from  the  Traders  pit,  or  (2)  they 
may  be  Traders  beds  which  have  escaped  the  severe  brecciation  to  which 
the  beds  in  the  Traders  and  Clifford  pits  have  been  subjected.  The  second 
suggestion  seems  to  be  the  more  plausible  one  because  of  the  short  distance 
intervening  between  these  pits  and  the  east  end  of  the  Traders  pit.  Even 
in  this  case  the  beds  must  be  separated  from  those  in  the  Traders  pit  by 
an  anticline.  , 

The  only  deposit  at  present  being  worked  in  this  area  is  that  of  the 
Clifford  pit.  Here  the  iron-bearing  rocks  are  the  same  as  at  the  Traders 
pit  (PI.  XXIV),  with  dark-gray  and  black  Traders  slates  to  the  east  and 
red  weathered  Brier  slates  to  the  west.  The  contact  between  the  iron- 
bearing  beds  and  the  underlying  slates  is  beautifully  exposed  on  the  east 
side  of  the  pit,  where  it  can  easily  be  followed  for  250  feet  or  more.  The 
upper  contact  of  the  iron-bearing  member  with  the  Brier  slates  can  also  be 
traced  on  the  stripped  surface  west  of  the  pit.  The  mapping  of  these 
contacts  shows  conclusively  that  the  rocks  are  plicated  into  several  minor 
synclines  and  anticlines,  and  a  study  of  the  relations  between  the  ore 
deposits  and  the  folds  show  that  the  richest  ore  is  in  the  synclines.  The 
best  ore  at  present  being  mined  is  taken  from  the  northeast  corner  of  the 
pit,  where  the  syncliue  in  the  underlying  slate  is  largest  and  most  typically 
developed  (see  map,  PI.  XXIV).     The  entire  area  occupied  by  the  pit  is 


ALGONKIAN,  THE  ORE  DEPOSITS.  409 

ore  producing,  but  the  ore  is  everywhere  richer  along  its  eastern — i.  e., 
lower — side  than  toward  its  western — i.  e.,  upper — side.  The  pitch  of  the 
folds  is  approximately  50°  NW.  The  greater  richness  of  the  Clifford  ore 
as  compared  with  that  from  the  Traders  pit  is  evidently  due  to  the  repeated 
folding  of  the  ore-bearing  beds  in  the  former  pit  and  the  consequent 
production  of  several  pitching  synclines  bottomed  by  the  black  slates. 

In  addition  to  being  folded,  the  iron-bearing  beds  are  deformed  by 
jointing  and  schistosity,  the  latter  structure  being  very  closely  related  to 
the  forrner.  The  schistosity  strikes  uniformly  N.  75°  to  80°  W.,  and  is 
therefore  in  some  places  parallel  to  the  bedding  and  at  other  places  ti-ans- 
verse  to  it.  Although  all  the  joints  strike  approximately  at  right  angles  to 
the  schistosity,  there  seem  to  be  two  sets  with  respect  to  dip.  In  one  set 
the  dip  is  about  50°  to  the  northwest,  and  in  the  other  20°  to  the  southeast. 
It  has  already  been  explained  that  the  brecciated  character  of  the  ore  beds 
in  this  pit  is  due  to  the  causes  that  produced  marked  schistosity  trans- 
verse to  the  bedding  (see  p.  302).  It  should  be  mentioned  in  addition  to 
what  has  already  been  stated  in  this  connection  that  the  mo.st  conglomeratic- 
looking  jaspilite  layers  are  found  on  the  north  side  of  the  pit,  where 
schistosity  and  bedding  are  approximately  perpendicular  to  one  another. 

The  nature  of  the  folding  south  of  the  Clifford  pit  and  between  this 
and  the  Cornell  pit  is  not  known,  as  there  ai'e  no  outcrops  in  this  area  and 
practically  no  explorations.  A  drift  running  about  northeast  from  the 
bottom  of  the  Fleischman  shaft  No.  1  (see  map,  PI.  XXIV)  to  a  point 
under  the  railroad  track  alongside  of  the  Traders  pit  was  driven  through 
ore-bearing  beds  tlu-oughout  nearly  its  entire  distance.  At  the  shaft,  how- 
ever, a  gray  quartzite  was  encountered  with  the  peculiarities  of  the 
quartzite  at  the  base  of  the  Traders  member.  No  explanation  of  its  occur- 
rence at  this  place  is  hazarded.  The  rock  may  be  a  locally  developed 
member  of  the  Traders  series.  The  wide  expanse  of  the  ore-bearing 
member  revealed  by  the  drift  suggests  its  repetition  by  folding,  and  the 
occurrence  of  ore  like  the  Clifford  ore  at  the  McClintock  exploration,  about 
600  feet  northwest  of  the  shaft,  suggests  that  at  least  one  of  the  folds 
extends  on  the  surface  to  this  point.  About  250  feet  north  of  the  McClin- 
tock exploration  is  a  pit  in  graphitic  slates  identical  with  those  at  the 
bottom  of  the  Hanbury  slate  south  of  the  southern  ore  belt. 

Nothing  is  known  of  the  rocks  in  the  intervening  distance.  The 
interval  is  scarcely  wide  enough  for  the  occurrence  in  it  of  both  the  Brier 


410  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

slates  aud  the  Cuny  member  with  their  normal  thickness.  Their  thick- 
ness, however,  might  be  much  diminished  on  the  sides  of  a  close  fold,  such 
as  must  exist  here  if  the  southern  pit  is  in  Traders  rocks,  and  both  mem- 
bers may  occur  in  the  interval  between  the  two  pits.  An  alternative 
theory  to  explain  the  structure  at  this  point  suggests  that  the  McClintock 
pit  is  really  in  Curry  beds  and  that  the  similarity  which  exists  between 
the  rocks  in  this  pit  and  those  of  the  Clifford  pit  is  due  to  the  fact  that  in 
both  instances  they  were  subjected  to  the  same  kind  of  close  folding  and 
shearing. 

CORNELL  MINE. 

The  Cornell  pit  at  present  affords  but  little  information  as  to  the  structure 
of  the  iron  formation  in  its  neighborhood.  It  has  not  been  worked  for  more 
than  ten  years  and  its  walls  have  in  many  places  become  covered  with  a 
talus  of  loose  material.  Enough  can  be  seen  of  the  rocks,  however,  to  show 
that  the  ore-bearing  beds  are  practically  identical  with  those  in  the  pits  of 
the  Traders  mine,  though  they  are  not  as  completely  brecciated  as  these. 
It  is  reported  that  a  "conglomerate  ore"  exists  to  the  north  of  the  western 
shaft  along  a  drift  running  north,  and  that  red  slates  occur  about  200  feet 
south  of  the  bottom  of  this  shaft  in  a  drift  running  about  south.  In  the 
northeast  portion  of  the  pit  there  are  indications  of  the  existence  of  folds  in 
the  ore-bearing  beds  (see  PI.  XXIV).  Near  its  northeast  corner  the  strike 
of  the  jaspilites  is  in  some  places  nearly  north.  Farther  west  the  strike  is 
N.  30°  W.  Somewhere  between  these  points  there  must  be  a  syncline 
pitching  to  the  south,  and  in  this  the  best  ore  would  be  expected  to  occur. 
As  a  matter  of  fact,  the  few  thousand  tons  shipped  from  this  mine  are 
reported  to  have  come  from  the  northern  part  of  the  pit.  There  are  also 
a  few  gentle  corrugations  visible  in  the  jaspilites  in  this  portion  of  the  pit. 
They  are  significant  only  as  indicating  that  the  beds  are  involved  in  larger 
folds  that  are  not  visible.  The  minor  corrugations  are  too  open  to  have 
afforded  distinct  channels  for  percolating  waters  aud  so  have  not  been 
efficient  in  determining  the  positions  of  ore  deposits.  The  absence  of  more 
distinct  folds  in  this  place  may  account  for  the  absence  of  a  larger  ore 
deposit. 

CUFF   MINE. 

At  the  Cuff  mine  the  exposures  are  not  sufficiently  abundant  to  disclose 
the  presence  of  sharp  folds  if  they  exist  in  its  vicinity  (PI.  XXV).  The  ore- 
bearing  rocks  are  very  similar  to  those  of  the  Traders  and  Cornell  mines,  but 


U    S. GEOLOGICAL    SURVEY 


MONOGRAPH    XLV!    PL. XXV 


LEGEND 
CAMBRIAN 


LakeSuperiorgandsione 
I  undfHyuip  fonnalu>n.i 
ahown  w/ifrr  hiitnvi,  / 


Test  pils,expasin^ 
only  sand»lone' 

ALGONKIAN 


Ah 


ilanbur>'  slate 


[K3 

Curry  member 
f  iwn-beanng  I 


RandviUe  dolomite 


Expo  sures.dip  and 
strike  not  shown 


epos ures  with  strike 
Dip  not  observed 


Expo  sureswtthobsened 
dipandatrikp 


Test  pits 


lol 

Mining  pits 


-Magnetic  declination 


Magnetic  dip 


Approximate  line  of . 
maximum  magnetic  dip 


GKOLOGIC  MAP  OF  THK  COUNTRY  ADJACENT  To  THE  CUFF  AND  INDIANA  MINES,  MKTIICAN 

SECS.  21,22,23.  26,  27,  AND  28, T.  40  N.,R.30W 

BY  W  SBAYl.EY 
1903 


looo  sou 


ALGONKIAN,  THE  ORE  DEPOSITS.  411 

tliey  are  apparently  less  brecciated  than  these.  In  the  open  pit  west  of  the 
shaft  the  strike  of  the  jaspilites  is  N.  10°  to  15°  W.,  and  their  dip  40°  N. 
(fig-.  17).  In  the  large  pit  east  of  the  shaft  the  strike  is  the  same  except  at 
the  southeast  corner,  where  it  is  N.  45°  E.  The  dip  in  this  pit  is  25°  N. 
East  of  this  again  is  a  small  pit  in  red  slates,  believed  to  be  at  the  base  of 
the  Traders  formation,  and  east  of  this  about  100  paces  is  a  trench  uncov- 
ering banded  ore  and  cherts  to  the  north  and  a  brecciated  ore,  like  that  at 
the  Clifford  pit,  to  the  south.  Southwest  of  the  shaft  a  number  of  openings 
have  been  made  disclosing  jaspilites  and  red  slates  with  a  wavy  contact  line 
between  them  that  suggests  the  presence  of  minor  folds. 

At  the  surface  just  east  of  the  shaft,  at  tlie  southwest  corner  of  the  pit 
already  referred  to,  is  a  white  or  lig'ht-gray  dolomitic  sandstone,  covering 
a  pinkish-gray,  even-banded  dolomite  dipping  45°  N.  Within  the  mine 
there  is  also  to  the  east  of  the  shaft,  according  to  the  testimony  of  the 
former  superintendent,  Mr.  Shephard,  a  "horse  of  white  soapstoue"  which 
upon  investigation  proves  to  be  a  dolomite.  This  is  on  the  first  level.  It 
does  not  reach  the  surface,  the  surface  rocks  above  it  being  contorted 
jaspilites.  The  great  northern  displacement  indicated  by  this  occurrence 
of  dolomite  in  the  mine  very  strongly  suggests  the  existence  of  a  fold  in 
this  rock  and  also,  of  necessity,  in  the  overlying  jaspilites.  The  fold  is  not 
sharp  and  well  defined,  and  consequently  the  ore  is  lean,  containing  from 
36  to  40  per  cent  metallic  iron. 

In  the  pit  to  the  east  of  the  shaft  the  relation  of  the  ore  to  the  folding 
and  crushing  of  the  jaspilites  is  well  exhibited  on  a  small  scale.  The 
jaspilites  exposed  in  this  pit  are  generally  flat  lying,  their  dip  being  about 
25°  N.  Toward  the  north  side  of  the  pit,  however,  the  rocks  are  bent  into 
a  small  monocline.  Here  they  are  crushed  into  breccias  and  here  also  the 
richest  ore  is  developed.  All  the  jaspilites  in  this  pit  are  characterized 
by  the  green  alteration  product  noted  in  connection  with  the  brecciated 
ores  of  the  Norway  and  other  mines  on  the  south  belt  (see  pp.  375  and  386). 

The  pit  lying  about  650  feet  west  of  the  shaft  encountered  an  evenly 
laminated  ferruginous  slate,  or  lean  ore,  devoid  of  jasper  bands.  It  is  placed 
in  the  Brier  belt  on  purely  petrographical  grounds. 


INDIANA    MINE. 


The  geology  of  the  environs  of  the  Indiana  mine  is  indicated  on  the 
map  (PI.  XXV).     The  plats  of  the  iinderground  workings  have  not  been 


412  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

seen.  The  results  of  drilling,  however,  give  no  indication  of  the  presence 
of  folds  in  the  vicinity  of  the  shaft,  the  output  of  which,  as  stated  above, 
was  only  about  18,000  tons.  The  rocks  on  the  dump  are  argillaceous 
Traders  slates,  even-banded  jaspilites,  brecciated  jaspilites,  and  even-banded 
ferruginous  slates  that  are  probably  Brier.  In  tlie  little  pit  opened  to 
the  west  of  the  shaft  the  argillaceous  slates  form  a  northern  wall  dipping 
south.  Even-banded  jaspilites  are  south  of  these,  on  the  northwest  and 
southeast  sides  of  the  pit.  The  dips  vary  slightly  in  different  places,  but 
no  distinct  folds  were  made  out  The  brecciated  ores  found  in  the  dump 
are  reported  to  occur  between  the  banded  jaspilites  and  the  slates.  North- 
west of  this  pit  and  at  a  distance  of  only  350  or  400  feet  is  a  ledge  of 
dolomite  with  a  strike  that  would  carry  the  rock  along  the  north  edge  of 
the  excavation.  Moreover,  drill  holes  put  down  south  of  the  mine  and 
directed  northward  encountered  dolomite  after  jjassing  through  Traders 
slates,  jaspilites,  and  Brier  slates  in  the  inverse  order  from  that  mentioned. 
At  the  contact  between  the  Traders  slates  and  the  dolomites  the  first-named 
rocks  were  everywhere  brecciated.  From  these  slight  data  it  is  thouglit 
probable  that  the  Indiana  deposit  is  a  contact  deposit,  like  that  of  some  of 
the  mines  on  the  southern  belt,  but  that  it  is  one  of  small  dimensions, 
because,  as  the  drill  holes  indicate,  the  dip  of  the  dolomite  flattens  out 
with  increasing  depth. 

FOREST    MINE. 

In  the  neighborhood  of  the  Forest  mine  the  exposures  of  pre-Cambrian 
beds  are  likewise  very  few  (fig.  33).  The  shaft  is  at  the  base  of  a  hill  which 
partially  encircles  it  on  the  north  and  east.  This  hill  is  capped  by  the  Lake 
Superior  sandstone  which,  of  course,  completely  hides  the  underlying  rocks. 
At  the  base  of  this  sandstone  is  a  conglomerate  varying  in  character  at 
different  places  in  such  a  way  as  to  show  that  the  dolomite  and  the  jaspilites 
continue  under  it  toward  the  east.  In  some  places  the  basal  layer  contains 
numerous  large  fragments  of  the  chert  that  often  occurs  at  the  top  of  the 
dolomite  formation.  At  other  places  the  principal  fragments  and  the  largest 
ones  consist  of  ore  or  of  jasper.  While,  therefore,  it  is  almost  certain  that 
the  two  formations  continue  for  some  distance  to  the  east  of  the  mine,  there 
is,  nevertheless,  no  evidence  to  indicate  how  far  they  extend.  A  few 
hundred  feet  northwest  from  the  mine  shaft  is  a  ledge  of  dolomite  forming 
a  little  cliff  to  the  south,  faced  by  a  veneering  of  sandstone  conglomerate. 


alCtOnkian,  the  ore  deposits. 


413 


At  the  base  of  'the  cHif  is  a  slate  band  dipping  70°  S.  This  is  exposed 
through  a  thickness  of  7  or  8  feet,  and  is  followed  to  the  south  by  jaspilites. 
The  sequence,  so  far  as  it  has  been  worked  out,  is  identical  with  that  at  the 
Indiana  mine.     The   mine  has  not  been  opened  up  sufficiently  to  yield 


8°^ 

Center 

6./ 

A 

.i            *.'  ■ .?-= 

9           '"    Forest  mine 

-"fc shaft 

T\           Os    -■-..... 

o      °  "y 

vr: 

•';•  . 

»"■•■■■... 

7° 

OSS 

sso 

s 
1 

\ 

6° 

\ 

X  "^ 

'I 

V 

o           

8°       %                            X 

7° 
6°                                                  7'                       3° 

i'4 

\ 

Kj 

Corner 

'•■ 

o  Teat  pits.        N   MuguetiL-  variation.  ^.^  .MagDetic  Jip.  o  Drill  lioles.         SS,  Sandstone.  S,  Slate.      J  ,  Jaspilite.        d  ,  Rand  ville  dolomite. 

Fig.  33.— Sketch  map  of  exposures  in  south  half  of  sec.  25,  T.  40  N.,  R.  30  W. 

important  geological  details.  There  is  no  evidence  at  present  of  the  presence 
of  a  fold  in  the  jaspilites  to  account  for  the  ore  deposit,  but  this  is  in  the 
normal  position  of  a  contact  deposit. 

THE  SOUTHERN  BELT. 

The  third  belt  of  ore  deposits  occurs  along  the  south  side  of  the  south- 
ern dolomite  belt,  and  extends  from  the  Menominee  River  on  the  west  to 
Waucedah  on  the  east.  It  includes  the  most  important  mines  in  tlie 
district  and  all  of  the  older  ones  that  are  still  being  worked.     All  the  mines 


414  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

that  are  at  present  productive  lie  between  Iron  Mountain  and  the  Sturgeon 
River. 

It  has  ah'eady  been  explained  that  the  southern  belt  of  dolomite  is  an 
anticlinoriuni.  Further,  it  has  been  pointed  out  that  superimposed  upon 
this  major  fold  are  folds  of  higher  orders  (see  pp.  237-246).  The  occurrences 
of  the  ore  deposits  in  the  Vulcan  formation  south  of  this  belt  of  dolomite  are 
closely  related  to  these  subordinate  folds.  The  folds  of  the  second  order 
superimposed  upon  the  major  fold  are  a  series  of  very  close  plications, 
which,  for  the  western  part  of  the  district,  plunge  steeply  to  the  west. 
The  result  of  these  plications  is  to  produce  a  number  of  westward-pitching 
synclinal  troughs  directly  underlain  by  some  jjhase  of  the  dolomite  foi'ma- 
tion  or  by  the  slates  of  the  Traders  member.  As  the  result  of  this  folding, 
the  surface  outcrop  of  the  southern  boundary  of  the  dolomite  has  a  notched- 
like  distribution,  producing  bays  in  the  dolomite.  The  iron-bearing  forma- 
tion occupies  the  bays  which  open  out  to  the  west  into  the  main  belt  of  the 
Vulcan  formation,  each  bay  being  surrounded  on  the  north,  south,  and  east 
by  the  dolomite. 

CHAPIN-PEWAKIC    DEPOSITS. 

Beginning  at  the  west,  the  first  and  most  important  set  of  folds  of  the 
second  order  are  those  adjacent  to  Iron  Mountain.  Here  are  two  important 
folds,  superimposed  upon  which  are  folds  of  the  third  order  (PI.  XXVIII). 
The  western  one  produces  the  troughs  in  which  the  Chapin,  Millie,  and 
Walpole  mines  are  located  (see  PI  XXVI,  A  and  B)  and  the  eastern 
one  the  trough  in  which  the  Pewabic  mine  occurs.  The  western  trough 
is  especially  complicated,  it  being  really  composed  of  two  minor  troughs 
or  folds  of  the  third  order,  with  an  intervening  anticline,  and  even  these 
folds  have  folds  of  a  higher  order  superimposed  upon  them.  If  one 
were  to  follow  a  geographical  order,  beginning  at  the  west,  the  Chapin 
mine  should  be  first  mentioned,  but  the  interpretation  of  the  occurrence  of 
the  ore  at  the  Chapin  mine  depends  upon  the  facts  furnished  by  the  Walpole 
and  the  Pewabic  mines.     They  are  therefore  first  considered. 

WALPOLE   MINE. 

The  Walpole  mine  has  a  north  and  a  south  ore  deposit  (fig.  34). 
These  ore  bodies  occur  in  subordinate  synclines,  separated  by  an  inter- 
mediate anticline.  The  synclines  and  the  anticline  together  constitute  the 
east  end  of  the  western  important  fold  <>f  the  second  order.     The  northern 


PLATE   XXVI. 


415 


PLATE     XXVI. 

VIEWS   OF   THE   CHAPIN   MINE. 

Fig.  ^4. — View  east  from  D  shaft,  Chapin  mine,  showing  shafts  on  Walpole-Chapin  fold.  Photo- 
graph liy  J.  J.  Eskil. 

The  shafts  to  the  left  of  the  sink  hole  are  the  C  and  the  B  shafts,  the  one  in  the  distance  at  the 
end  of  the  sunken  ground  is  the  abandoned  A  shaft,  and  that  in  the  foreground  is  the  D  shaft  of  the 
Chapin  mine.  The  top  of  No.  2  shaft  can  be  seen  projecting  above  the  roof  of  the  engine  house 
connected  with  the  D  shaft.  The  mine  in  the  notch  on  the  top  of  the  hill,  nearly  in  the  center  of  the 
view,  is  the  Millie  mine,  and  that  in  the  far  distance  to  the  left  is  the  Walpole  mine.  The  Pewabic 
mine  is  over  the  hill  to  the  right  of  the  Millie  mine.  The  hill  behind  the  A  shaft  is  composed  of 
Randville  dolomite,  topped  by  horizontal  layers  of  sandstone.  The  knob  to  the  right  is  Hughitt 
Bluff.  It  consists  of  evenly  banded  Traders  jaspilites.  The  gully  to  the  south  of  the  C  and  B  shafts 
was  caused  by  settling  of  the  ground  in  consequence  of  removal  of  the  ore. 

Fig.  B. — View  west  from  A  shaft,  Chapin  mine,  showing  distribution  of  shafts  on  Chapin  prop- 
erty.    Photograph  by  J.  J.  Eskil. 

B  and  C  shafts  are  to  the  right,  No.  2  shaft  to  the  left,  and'  D  shaft  at  the  end  of  the  large  sink  hole. 
In  the  distance,  to  the  left  of  the  second  sink  hole,  is  the  Ludington  shaft.  The  shaft  to  the  right  of 
the  B  shaft  is  the  Hamilton  shaft.  The  sink  holes  are  produced  by  the  settling  of  the  ground,  due  to 
the  removal  of  the  ore  from  beneath. 

"  The  hill  in  the  distance  is  Prospect  Bluff. 

416 


U.   S.   GEOLOGICAL  SURVEY 


MONOGRAPH  XLVl       PL.    XXVI 


A.      VIEW    EAST    FROM    D   SHAFT,    CHAPIN    MINE,    SHOWING   SHAFTS    ON    WALPOLE-C  H  AP I N    FOLD. 


B,     VIEW   WEST   FROM   A  SHAFT,    CHAPIN    MINE,   SHOWING    DISTRIBUTION    OF  SHAFTS  ON    CHAPIN    PROPERTY. 


ALGONKIAN,  THE  ORE  DEPOSITS. 


417 


deposit  is  an  excellent  illusti-ation  of  a  steep  joitching  trough  which  is 
bottomed  by  slate  and  dolomite,  and  is  bounded  on  all  sides  but  one  by  the 
same  rocks.  The  fold  is  here  so  close  that  the  iron-bearing  member  on 
the  south  limb  has  all  but  been  pinched  out.  The  southern  ore  body  is  just 
as  clearly  in  a  westward-pitching  syncline.  Shaft  No.  2  of  the  "Walpole 
mine  is  on  its  southern  side  at  the  contact  of  the  iron-bearing  rocks  with  the 
underlying  dolomite,  and  the  Millie  mine  is  near  the  center  of  its  southern 
limb  farther  west.    The  workings  of  the  Walpole  mine  beautifully  illustrate 


-No.l  SHAFT 


Fig.  34.— Horizontal  .section  of  the  Walpole  mine  at  the  thircl  level. 


the  relation  and  succession  of  the  formations  Avhich  occur  between  the  lime- 
stone and  the  Brier  slate  in  places  where  the  folding  is  of  a  verv  com- 
plicated character. 

The  ores  of  the  Walpole  mine  and  the  Millie  mine  are  often  brecciated 
to  a  remarkable  extent.  The  fragments  of  the  rock  are  cemented  together 
either  by  subsequently  deposited  ore  or  by  drusy  masses  of  a  yellowish 
dolomite.  This  is  especially  true  of  the  ores  in  the  eastern  ends  of  the  folds 
where  they  are  closely  compressed.     The  brecciated  ores  are  beautifully 


MON    XLVI — 04- 


-27 


418 


THE   MENOMINEE  IRON-BEAKING  DISTRICT. 


exposed  on  the  walls  of  the  long  crosscut  tliat  connects  the  workings  of 
the  two  shafts. 


PEWABIC    MINE. 


The  Pewabic  mine  is  on  a  single,  closely  compressed  fold  (fig.  35).  The 
slate  and  dolomite  are  here  again  found  on  the  north,  east,  south,  and  at  the 
bottom  of  tlie  ore  body.  Here,  however,  on  the  south  limb  of  the  fold  the 
ore-bearing  member  does  not  ajjpear  between  the  dolomite  and  the  Brier 
slate.  It  has  therefore  been  squeezed  out  by  the  very  great  pressure,  or 
else  slight  faulting  has  taken  place.  A  crosscut  north  on  the  first  level 
from  the  ore-bearing  Traders  bed  to  the  limestone  shows  several  repetitions 
of  the  foot-wall  slates,  the  quartzite,  and  the  iron-bearing  members,  these 
being  found  in  narrow  belts  (fig.  36).  The  reduplications  are  regarded  as 
due  to  very  close  subordinate  folding.  The  thickness  of  the  Brier  slate  as 
developed  on  the  surface  by  test  pitting  in  the  vicinity  of  the  Walpole  shaft 


Trade, 


^f-Ho.  2  SHAFT 
-■"  Scale 

0 200 400 600  feet 

Hanbury  slate 

Fig.  35. — Horizontal  section  of  the  Pewabic  mine  at  the  third  level. 

No.  3  (see  map,  PI.  XXYIII),  seems  to  confirm  this  view.  The  succession 
of  beds,  so  far  as  they  could  he  seen  at  the  time  the  section  was  examined, 
is  indicated  in  the  figure.  The  talcose  .slates  are  typical  light-colored  ser- 
pentinous,  or  talcose  Traders  slates.  The  quartzites  are  like  those  near 
the  base  of  the  Traders  formation  elsewhere,  and  some  beds  are  conglom- 
eratic. Toward  the  south  side  of  the  section  there  is  a  series  of  banded 
jaspilites,  which  for  118  feet  south  of  their  contact  with  the  Brier  slate 
appear  to  be  continuous.  To  the  south  of  this  jjoint,  however,  they  are  cut 
by  seams  of  the  Lake  Superior  sandstone,  and  contain  irregular  pockets  of 
the   same   sand   rock.      Gradually  the  jaspilites   diminish   in   quantity,   the 


ALGONKIAN,  THE  ORE  DEPOSITS. 


419 


sandstone  increasing  at  the  same  time,  nntil  finall}-  the 
jaspiHtes  appear  as  distinct  bowlders  and  fragments  hi 
the  sandstone,  and  the  rock  becomes  a  typical  ore  con- 
arloraerate  at  the  base  of  the  Cambrian.  The  transi- 
tion  from  the  bedded  jaspilites  to  the  ore  conglomerate 
is  so  gradual  that  it  is  not  possible  to  recognize  a  dis- 
tinct line  of  demarcation  between  them.  The  conglom- 
erate was  evidently  deposited  immediately  upon  the  rock 
which  yielded  its  bowlders.  The  surface  upon  which  it 
was  laid  down  was  made  up  of  the  ends  of  vertical  lay- 
ers of  the  jaspilites,  which  were  fractured  and  shattered, 
and  in  which  joints  had  been  opened  by  weathering. 
Into  the  latter  sand  liad  filtered  and  formed  the  veins, 
seams,  or  dikes  noted  as  cutting  the  jaspilites  in  the  drift. 
The  shattered  parts  were  cemented  by  small  quantities 
of  sand  that  sifted  down  between  the  loose  fragments. 
Near  the  surface  of  the  unshattered  rock  the  fragments 
had  not  been  much  disturbed  in  their  position,  and  the 
sand  consequently  appears  as  pockets  in  a  solid  rock. 
Farther  away  from  the  solid  surface  the  fragments  were  * 
more  separated.  A  greater  (piantity  of  sand  sifted  down  v& 
between  them,  and  made  a  well-defined  conglomerate.  | 
At  the  extreme  southern  end  of  the  drift  the  conglom-  -" 
erate  passes  into  a  pure  sandstone.  z 

A   second  drift  passing  north  from  the  main  ore-    1 
bearina:  belt  on  the  third  level  toward  the  dolomite  near    s 
the  east  end  of  the  fold  (see  fig.  35)   shows  a  similar    i- 
alternation  of  talcose  or  serpentinous  slates,  quartzites,    S' 
and  an  ore  bed.     A  drill  hole,   put   through  the  Brier 
slates  south  of  the  ore-bearing  beds  and  starting  at  a 
point  nearly  opposite  the  mouth  of  the  crosscut,  passed 
through  a  small  thickness  of  the  slates  and  immediatel}" 
thereafter  entered  a  bed  of  Traders  quartzite.     The  ore- 
bearing'  bed  encountered  on  the  south  side  of  the  Brier 
slates  farther  west  (see  fig.  35)  is  not  met  with  at  the 
east  end  of  the  fold,  nor  is  its  manner  of  disappearance 
known.     It  is  believed,  however,  to  have  disappeared  by  faulting 


3  -» 


along 


420  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  contact  plane  between  the  Randville  dolomite  and  the  Upper  Menomi- 
nee series.  There  is  a  well-defined  fault  on  the  fourth  and  lower  levels  of 
the  mine  between  the  Brier  slate  and  the  ore  formation,  Imt  whether  this 
is  a  continuation  of  the  fault  on  the  contact  line  at  the  east  end  of  the  mine 
or  not  has  not  been  determined. 

It  is  thus  plainly  seen  that  the  ore  of  this  mine  is  in  a  sharply  com- 
pressed synclinal  fold  that  pitches  to  the  Avest.  The  sjmcline  becomes 
flatter  with  depth,  but  it  continues  to  pitch  westward  as  far  as  mining-  has 
progressed.  In  a  publication  to  which  reference  has  already  been  made, 
Mr.  E.  F.  Brown  reports  the  higher  phosphorus-bearing  ore  to  be  toward 
the  bottom  of  the  fold. 

CHAPIN   MINE. 

At  the  present  time  the  workings  of  the  Chapin  mine  have  not 
extended  sufficiently  far  to  disclose  beyond  question  the  relations  of  the 
ore  bodies.  As  yet  these  have  not  been  connected  underground  with  the 
ore  deposits  of  the  Walpole  in  such  a  manner  as  to  show  the  continuity  of 
the  Chapin  folds  with  those  of  the  Walpole  mine.  However,  two  main 
belts  of  ore  have  been  developed  at  the  Chapin  mine,  and  it  is  believed 
that  the  northern  belt  of  ore  will  be  found  to  correspond  Avith  the  northern 
fold  of  the  Walpole  mine  and  the  southern  belt  with  a  subordinate  fold 
in  this. 

North  of  the  northern  ore  body  is  a  succession  of  slates  and  quartzites 
similar  to  that  north  of  the  Walpole  and  the  Pewabic  shafts.  A  slate  with 
the  characteristics  of  the  Brier  slate  occurs  between  the  two  belts  of  ore 
bodies  and  a  similar  slate  bounds  the  southern  ore  lens  on  the  south. 
South  of  this  slate  is  a  wide  iron-bearing  formation  which  is  apparent]}"  con- 
tinuous with  the  Millie  and  South  AValpole  belt,  and  south  of  this  again  are 
slates  and  quartzites  that  are  believed  to  be  the  westward  continuation  of 
the  Brier  slate  belt  of  the  Pewabic  mine  (see  fig.  37).  The  south  ore  lens 
at  the  cross  section  given  in  the  figure  is  bounded  by  slate  above  as  well 
as  below.  The  explanation  of  this  anomaly  is  probably  that  the  compres- 
sion was  so  severe  that  the  lower  portion  of  the  ore-bearing  bed  was  actually 
pinched  out,  the  slate  on  each  side  of  the  ore  coming  together.  The  same 
is  true  of  the  top  of  the  new  south  lens  of  ore,  the  upper  part  of  which  is 
inclosed  by  slates. 


U  5   GEOLOGICAL   SURVEY 


GRAPH    XLVl      PL 


Hamillon    Shaft 


OlTl.INKS  OFOHK  BODIES 
IX  FI1"I"I  I ,  S  IVril.  SE\-KNTH„\NI)  TlvXTl I 
("HAPIN  MINK 


•:\'ELS 


ALGONKIAN,  THE  ORE  DEPOSITS. 


421 


It  is  impossible  at  present  to  be  absolutely  sure  as  to  the  horizon  at  which 
the  great  lenses  of  ore  of  the  Chapin  belong,  although  they  are  apparently 
all  of  tlie  same  age.  Since,  however,  the  relations  of  the  ore  bodies  to  the 
surrounding  rocks  at  the  Chapin  are  parallel  in  many  particulars  to  the  occur- 
rences at  the  Walpole  mine,  and  since  the  northern  ore  belt  is  continued 


HAMILTOH 
North     SHAFT  Ho£^ 


D  SHAFT,  CHAPIN 


Fig.  37.— Vertical  north-south  cross  section  through  D  shaft,  Chapin  mine. 

eastward  by  jaspilites  beyond  the  east  end  of  the  old  north  lens  toward  the 
Walpole  deposit,  it  is  thought  that  the  two  ore  belts  belong  to  the  Traders 
member  of  the  iron-bearing  formation,  that  member  being  repeated  by 
close  folding.  According  to  this  explanation,  each  of  the  two  northern  ore 
lenses  would  constitute  the  north  limb  of  a  synclinal  fold,  separated  from 


422 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 


the  southern  belt  of  lenses,  which  must  be  anticlinal,  by  a  syncline  of  slates 
corresponding  to  the  syncline  of  the  same  rock  in  the  northern  part  of  the 
Walpole  area.  The  belt  of  slate  south  of  the  southern  ore  lenses  would  also 
be  synclinal,  con-esponding  to  the  syncline  in  the  southern  portion  of  the 
Walpole  area.  This  structure  would  fix  the  position  of  the  next  southern 
iron-bearing  belt,  in  which  no  large  ore  bodies  have  been  found,  as  an  anti- 
cline of  Traders  beds.  The  slates  and  quartzites  south  of  this  would  be 
Brier,  and  the  southern  belt  of  iron-bearing  formation  would  be  a  monocline 
of  the  Curry  formation.     Because  of  its  monoclinal  character,  ore  bodies 


Fig.  38.— Vertical  north-south  cross  section  through  No.  2  and  C  shafts,  Ohapin  mine. 

are  wanting  in  this.      Following  the  southern  jaspilite  series  to  the  south 
are  the  Hanbury  slates. 

The  isoclinal  folds  at  the  Chapin  mine  are  overturned;  the  axial  planes 
dip  to  the  north  and  pitch  to  the  west  (PL  XXVII).  The  dolomite,  which 
belongs,  stracturally,  below  the  Vulcan  formation,  really  rests  upon  it  with 
a  steep  northern  dip,  about  80°  at  the  surface,  but  bending  so  as  to  be  as 
low  as  70°  deep  in  the  mine.  For  a  long  time  it  was  a  question  with  the 
miners  which  of  the  two  formations  was  geologically  the  higher.     How- 


U.  S.  GEOLOGICAL  SURVEY 


MONOGRAPH  XLVI     PL. XXVIII 


LEGEND 
ORDOVICIAN 


Hermansvillelimeetone 
CAMBRIAN 


LakeSuperiorsandalone 
<  ujideHytng  /brmaitoru 
shown  wKerr  known  ) 


GEOLOGIC  MAP  OF  THE  CHAPIN-l'tiWABIC  FOLDS,  MICHIGAN 

PARTS    OF    SECS.    29,30,  31, AND    32,  T.  40  N.,  R.  30W" 
BYW,  S.BAYLEY 
1903 
Scale 
500  q '""  I  -inn zooofeet 


Pits  exposing 
only  sandstone 

ALGONKIAN 


Hanbury  slate 


Slate  in'fradera  member 
RandviUe  dolomite 


Exposures, dip  and 

strike  not  shown 

'attL  ake  Superiorsandstone 

crposiirea  are  horizontal  i 


[ID 


lExposures  with  strike 
Dip  not  obser\-ed 


Exposureswithobserved 
dip  and  strike 


Test  pits 


lOl 

Mining  pits 


Magnetic  dip 


c::5 


Boundan-of 
sunken  ground 


ALGONKIAN,  THE  ORE  DEPOSITS.  423 

ever,  the  occurrence  of  undoubted  dolomite  bowlders  in  the  Traders  member 
and  the  continuity  of  the  dolomite  from  the  vicinity  of  Iron  Mountain  to 
the  east  end  of  the  district  have  shown  beyond  question  that  the  dolomite 
is  the  lower  formation.  With  the  possible  exception  of  the  Quinnesec,  the 
Chapin  mine  shows  the  most  intense  folding  known  in  the  district,  the  struc- 
ture being,  in  short,  a  set  of  isoclinal  overturned  folds. 

If  the  above  be  the  correct  explanation  of  the  structure,  the  Chapin 
and  Millie  mines  (see  map  and  section,  PI.  XXVIII)  present  a  case  of 
isoclinal  folding,  the  strata  of  which  are  reduplicated  three  times,  not  to 
mention  the  minor  duplications  north  of  the  northern  lens  of  ore.  While  it 
is  freely  admitted  that  as  yet  this  interpretation  has  not  been  proved  to  be 
the  trvie  one,  it  is  the  one  which  on  the  whole  appears  to  correspond  most 
closely  with  the  facts. 

This  explanation  of  the  structure  is  different"  from  that  proposed  in 
the  preliminary  report  on  the  district,  which  regarded  the  lenses  of  ore  in 
the  Chapin  mine  as  structural  synclines  and  the  slates  between  them  as 
anticlines.  More  mature  consideration  of  the  facts  known  at  the  time  the 
previous  report  was  written  and  a  better  knowledge  of  some  facts  not  fully 
appreciated  at  that  time  seem  to  render  the  former  theory  of  the  structure 
imtenable. 

The  lenticular  shape  of  the  ore  bodies  in  the  Chapin  mine  is  explained 
as  due  to  pinching  out  of  the  formation  by  the  intense  folding.  Lens- 
shaped  masses  of  the  iron-bearing  formation  became  entirely  or  nearly 
entirely  surrounded  by  slates  and  thus  were  practically  in  basins  with 
impervious  bottoms. 

If  the  structure  as  outlined  above  is  correct,  there  should  be  a  tongue 
of  the  southern  belt  of  the  iron-bearing  Traders  beds  projecting  eastward 
into  the  Brier  slates  opposite  the  southern  ore  lens  at  shaft  D.  This  portion 
of  the  area  has,  however,  not  been  thoroughly  explored,  and  any  statement 
as  to  the  existence  of  such  a  tongue  at  that  place  would  be  unwarranted  at 
the  present  time. 

OLD    KEEL    RIDGE    MINE. 

The  old  Keel  Ridge  mine,  situated  in  the  northeast  quarter  of  the 
southwest  quarter  of  sec.  32,  T.  40  N.,  R.  30  W.,  was  abandoned  prior  to 
1885.  During  its  active  life  it  shipjaed  about  60,000  tons  of  ore.  There  are 
a  number  of  open  pits  and  tunnels  surrounding  the  main  shafts,  but  their 

^Geologic  Atlas  U.  S.,  folio  62,  U.  S.  Geol.  Survey,  1900,  pp.  7-8. 


424  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

condition  is  not  such  as  to  afford  favorable  opportunities  for  study  (Pis. 
XXVIII  and  XXIX).  The  rocks  exposed  in  these  openings  are  jaspilites, 
with  red  fissile  slates  to  the  south.  The  slates  in  many  instances  look  very 
much  like  the  Brier  slates,  but  in  other  instances  they  are  like  the  typical 
sericite-slates  of  the  Hanbury  formation.  The  jaspilites  resemble  more 
closely  the  Curry  jaspilites  than  those  of  the  Traders  member.  They  are 
frequently  evenly  banded  and  cherty,  and  in  a  few  cases  their  siliceous 
bands  are  gray  cherts  containing  streaks  and  shots  of  ore.  The  general 
dip  of  the  beds  appears  to  be  to  the  north  at  about  70°,  but  departures  from 
this  are  common.  The  ore  is  on  the  foot-wall  side  of  the  iron-bearing 
member  at  its  contact  with  the  slates.  These  are  stratigraphically  above 
the  ore-bearing  beds,  but  the  overturn  of  the  series  to  the  north  places 
them  underneath  the  ore  Moreover,  the  iron-bearing  beds  are  strongly 
contorted  (see  fig.  24,  p.  357),  furnishing  many  little  synclines  in  which  the 
ore  may  have  been  concentrated.  These  pitch  westward  at  low  angles,  a 
few  of  those  measured  varying  in  pitch  between  17°  and  20°.  It  is 
probable  that  the  deposition  of  ore  at  this  place  in  larger  quantity  than  at 
any  other  place  in  the  practically  straight  course  of  the  Vulcan  formation 
between  the  Pewabic  and  Quinnesec  mines  was  due  to  the  contortion  of 
the  beds,  which  was  doubtless  connected  with  the  sharp  turn  of  the 
formation  around  the  anticline  of  dolomite  between  the  Keel  Ridge  and 
the  Pewabic  mines. 

Between  the  Keel  Ridge  area  and  the  Pewabic  mine  to  the  north 
there  should  be  an  anticline  of  the  Vulcan  beds  over  the  Randville 
dolomite  which  separates  the  Pewabic  fi'om  the  Keel  Ridge  deposits. 
Absolutely  nothing  is  known  of  this  area,  in  which  the  Huronian  rocks  are 
bui'ied  beneath  thick  deposits  of  the  Cambrian  sandstone;  consequently  on 
the  map  (PI.  XXVIII)  it  is  left  uncolored. 

KEET.  RIDGE  MINE. 

The  present  Keel  Ridge  mine  is  in  the  southeast  quarter  of  the 
southeast  quarter  of  sec.  32,  T.  40  N.,  R.  30  W.,  about  three-fourths  of  a 
mile  east  and  a  little  south  of  the  old  Keel  Ridge  workings  (PI.  XXIX). 
Prior  to  1900  the  shipments  from  this  mine  amounted  to  33,636  tons.  The 
ore  is  highly  siliceous  (see  analysis,  p.  382).  The  ore-bearing  series  consists 
of  even-  and  thin-bedded  cherty  jaspers  and  ore  bands  striking  about 
N.  56°  W.,  and  dipping  75°  to  85°  N.     Following  this  to  the  south  are 


U    S    GEOLOGICAL   SURVEY 


MONOGRAPH   XLVI      PL    XXIX 


i^)^^i 


S  B1F.N  *CO   Ln 


LEGEND 

CAMBRIAN 


LakeSuperiorsandstone 

( luuieriyiTt^  lor/n  a  liorLs 
sliown  where  known  J 


Test  pits. exposing 
onlvsandstone 


ALGONKIAN 


[Z3 
Hanbury  slate 


Ciirry  member 

( trori-'oearuig  / 

Ab" 


Ar 


Rail  dville  dolomite 


Exp9sures,dip  and 

strike  noi  shown 

I  ail  Lake  SuperLor sandstone 

exposures  are  horizontal  t 


Exposures  witli  strike 
Bip  not  observed 


Exposures  with  observed 
dipandstrike 


Shafts 
Test  pits 
Drill  holes 

\^\  " 

Minintf  pits 


Tunnels 


Magnetic  dip 


GEOLOUK    MAP  xVND   S  PACTION 

SE.  "4  SECTION  32.<\NDA  PORTION  OFAIIJACENT  SECTION  33, T.  40  N..K. 30  W., MICHIGAN 

BYAV.  S.BAYLEV 
1903 
Scale 
soo  0  500  lODofeet 


^G\.e:'nie  data  for  t/if  section  were  furnished  bythemafiaffcmjenl  of 
theS'ewabi^'  rninj^.  Th£  topographic  features  a-re  unduly  ej:a{jgercLted 


alCtOnkian,  the  ore  deposits.  425 

mottled  and  gray  slates  of  tlie  Haiibury  foi-mation.  To  the  north  there  are 
no  exposures  of  any  kmd  until  the  cliff  of  cherty  dolomite  overlain  by  sand- 
stone is  reached  (see  p.  262).  Between  this  point  and  the  open  mine  pit 
there  is  abundant  room  for  the  presence  of  a  slate  formation,  and  in  a  drill 
hole  on  the  section  line  nearly  east  of  the  open  pit  a  slate  was  obtained. 
In  the  cross  section  this  slate  is  indicated  as  being  Brier,  and  the  dolomite 
is  made  to  extend  about  350  feet  south  of  its  southern  exposure  on  the  sur- 
face. The  data  are  woefully  deficient  for  determining  the  structure  of  the 
area,  but  tliey  are  perhaps  sufficiently  full  to  shoAV  that  folding  is  lacking.- 
There  is  no  noticeable  breeciation  of  the  ore-bearing  beds  in  the  mine,  and 
so  far  as  can  be  determined  no  definitely  marked  ore  deposit  has  yet  been 
encountered.  All  the  ore  that  can  be  seen  from  the  surface  consists  merely 
of  particularly  rich  portions  of  the  jaspilite. 

QUINNESEC,    CUNDY,    AND    VIVIAN    MINES. 

The  next  important  point  to  the  east  of  the  Pewabic  mine  where  ore 
is  produced  is  at  Quinnesec.  Here  there  are  three  mines,  the  Quinnesec 
mine,  north  of  the  callage  of  Quinnesec;  the  Cundy  mine,  on  its  western 
outskirts;  and  the  recently  opened  Vivian  mine,  northwest  of  the  village 
and  about  one-fomth  mile  west  of  the  Quinnesec  mine.  Between  the  Quin- 
nesec and  the  Cundy  mines  are  three  belts  of  jaspilites  and  three  belts  of 
slate  with  the  physical  characters  of  the  Brier  slate.  These  belts  can  be 
traced  westward  by  test  pits  and  trenches  for  a  distance  of  over  one-half 
mile,  but  toward  their  ends  explorations  are  scarce  and  the  exact  manner 
of  the  termination  of  all  the  belts  is  not  known  (see  map,  PI.  XXX).  Drill 
holes  a  fcAV  hundred  feet  west  of  the  west  line  of  sec.  34  seem  to  show  that 
beyond  this  line  the  three  belts  of  jaspilite  are  reduced  to  one.  About  one- 
half  mile  east  of  the  east  line  of  the  section  the  entire  Vulcan  formation  is 
absent.  The  disappearance  of  the  whole  or  a  large  part  of  the  formation 
both  to  the  east  and  the  west  of  sec.  34  is  explained  by  the  overlap  of  the 
Hanbury  slates. 

The  scarcity  of  exposures  and  explorations  east  of  the  line  joining  the 
Gray  shaft  of  the  Cundy  mine  and  the  east  shaft  of  the  Quinnesec  mine, 
and  in  the  western  portion  of  the  area,  for  a  distance  of  600  feet  on  both 
sides  of  the  section  line  between  sees.  34  and  33,  renders  the  interpretation 
of  the  geology  at  this  place  very  doubtful.  It  is  known,  however,  that  the 
boundary  of  the  Raudville  dolomite  southeast  of  the  Quinnesec  mine  is 


426  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

indented  by  a  reentrant  extending  eastward.  This  is  interpreted  as  indicating 
a  synclinal  fold  pitching  to  the  west  (see  p.  239).  With  this  as  a  starting 
hypothesis  a  reasonable  explanation  of  the  geology  of  the  district  would 
appear  to  be  as  follows :  The  ore  of  the  Quinnesec  mine  and  the  quartzites 
and  slates  between  it  and  the  dolomite  to  the  north  belong  in  the  Traders 
member,  which  at  this  place  is  the  north  limb  of  a  syncline  overturned  to  the 
south  (see  sections  D-D  and  C-C).  South  of  this  is  a  narrow  sjoicline  of  the 
Brier  slates,  and  to  the  south  of  this  an  anticline  of  Traders  beds.  Fol- 
lowing this  belt  in  succession  toward  the  south  are  a  syncline  of  Brier  slates, 
another  anticline  of  the  Traders  member,  and  a  succession  of  Brier  slates, 
the  Curry  member,  and  the  Hanbury  slates  in  a  southward-dipping  mono- 
cline. This  structure  would  place  the  Cundy  deposit  in  the  Curry  member. 
At  about  the  west  line  of  the  section  the  northern  belt  of  the  Traders  mem- 
ber disappears  by  overlap  and  the  second  and  third  belts  by  the  westward 
pitch  of  the  anticlines.  The  third  belt  bifurcates  near  the  north-south  line 
of  sec.  34.  Its  northern  limb  unites  with  the  western  end  of  the  second 
belt  and  disappears,  as  explained,  by  an  anticline  plunging  beneath  the 
ovei'lying  slates.  The  narrow  syncline  of  slate  immediately  south  of  the 
Quinnesec  ore  deposit,  according  to  this  view  of  the  structure,  is  canoe 
shaped  and  is  terminated  at  both  ends  by  inclosing  syuclines  of  the  under- 
lying Traders  beds.  The  identification  of  this  slate  as  Brier  rests  on  purely 
lithological  evidence. 

The  second  belt  of  slates  is  also  a  canoe-shaped  syncline  which  terminates 
both  to  the  east  and  to  the  west  by  anticlines.  West  of  the  west  end  of 
this  belt  is  another  small  area  of  slates  separated  from  the  main  belt  by  an 
anticline  of  the  underlying  jaspilites.  The  third  belt  of  slates  stretches 
west,  wraps  around  the  end  of  the  southern  portion  of  the  southern  belt  of 
Traders  jaspilite,  makes  a  salient  between  the  bifurcating  legs  of  the  south- 
ern jaspilite  belt,  and  surrounds  the  western  end  of  the  northern  jaspilite 
anticline  at  this  place.  Thus,  at  the  quarter  line  of  the  section  there  are 
four  jaspilite  belts  and  four  slate  belts,  and  a  little  farther  west  there  are 
but  three  of  each. 

Beyond  the  point  at  which  the  jaspilite  belts  disappear  there  are  no 
exposures  for  some  distance,  but  one-fourth  mile  beyond,  several  drill 
holes  reveal  the  presence  of  a  jaspilite  belt  between  talcose  slates  to  the 
north  and  a  thick  series  of  slates  on  the  south  that  are  supposed  to  belong 
in  the  Hanbury  formation.     This  belt  of  jaspilite  is  con-elated  with  the 


U.S.  GEOLOGICAL   SURVEY 


MONOGRAPHXLVI      PL. XXX 


LEGEND 

CAMBRIAN 


liakc  SujMfhorsandstonc 

Shuwri  v^herr  kritrrfn  I 


Test  pitB.exposiiii 
onh' sandstone' 

ALGONKIAN 


Ah 


Hanbur\'  slal*^ 


Curry  member 

/  irvri  tifarin/f  I 


Atj 


Jaspilnein 
Tradeis  member 

,  ir\tn  heariruf  I 


SlaU-:inJqu.trtzilr 
inTraders  (nemU-r 


RandviUe  dolomiie 


Exposures. dip  and 

strike  not  shown 

ioIlL  ake  Sup  eriorsandstone 

exposures  are  horixontal  > 


Exposures  with  slrilw 
Dip  iiol  observed 


E  xposu  res  wi  th  observed 
dipand  strike 


Test  pits 


Drill  holes  shelving 
direction  and  length 


YMER  SHAFT 


V  V  AN       MINE 


€ls         A    B    Ah         Ac  Ab      At]       Ab         At 


CIS         B'     C       Ah 

\      %  ' 


GEOLOGIC  MAP  AND   SECTIONS  OF  QUINNESEC  AREA,  MICHIGAN 


B^'\^'.  S.BAYL,EY 
1903 
Scale 
soo  lOOO 


LI 


Mining  pits 


2000  feet 


ALGONKIAN,  THE  ORE  DEPOSITS.  427 

Ciiny  belt  farther  east,  in  which  the  Cundy  mine  is  opened  u\).  There  is 
no  evidence  as  to  the  manner  of  disappearance  of  the  northern  jaspiHte  belt 
or  of  the  wide  slate  belt  formed  by  the  merging  of  the  three  slate  belts 
noted  in  the  eastern  portion  of  the  area.  The  disappearance  is,  however, 
supposed  to  be  due  to  overlap  and  the  boundary  lines  between  the  belts  are 
drawn  accordingly. 

The  structure  of  the  Quinnesec  area,  as  indicated  by  the  explorations, 
is  represented  on  the  map  (PI.  XXX)  and  the  four  cross  sections.  It  will 
be  noticed  that  while  the  area  as  a  whole  is  a  westward-pitching  synchno- 
rium  with  three  closely  compressed  and  overturned  east-west  folds,  it  is  also 
affected  by  two  broad  north-south  folds,  the  synclines  of  which  are  indicated 
by  the  broader  portions  of  the  slate  belts  and  the  anticlines  by  the  entire 
disappearance  of  these  and  the  appearance  of  the  wider  portions  of  the 
jaspilite  belts. 

The  Quinnesec  ore  body,  according  to  this  view,  is  a  narrow  deposit 
at  the  contact  of  a  thin  series  of  jaspilites  with  a  bed  of  slates  that  underlie 
them  in  position,  though  overlying  them  stratigraphieally.  The  dolomite 
and  the  talcose-schists  at  this  locality  apparently  overlie  the  ore,  the  dip 
being  about  70°  N.  The  ore  is  bounded  by  the  talc-schists  on  the 
north  and  by  slates  on  the  south.  South  of  these  slates  is  an  iron-bearing 
formation.  The  ore  in  longitudinal  section  passes  into  jaspilites  both  to 
the  east  and  to  the  west.  To  the  east  is  the  sharp  embayment  in  the 
underlying  dolomite  which  suggests  a  corresponding  westward-pitching 
fold  in  the  adjacent  iron  formation.  The  Quinnesec  deposit  is,  therefore, 
on  the  north  side  of  a  pitching  trough.  Southeast  of  the  easternmost 
shaft  of  the  mine,  on  the  south  side  of  tlie  tranu'oad  from  the  mouth 
of  the  pit,  is  a  large  exposure  of  jaspilites  showing  very  complicated  con- 
tortions that  are  in  many  instances  extremely  sharp.  These  indicate  close 
and  complicated  folding  of  the  iron-bearing  member,  but  throw  little  light 
on  the  exact  character  of  the  folding. 

The  Cundy  deposit  is  in  the  southernmost  ore-bearing  belt.  This 
is  a  monocline  dipping  south  at  from  70°  to  80°.  Tlie  ore  is  hard  and 
lean  and  contains  considerable  magnetite.  No  distinct  jaspilites  have  been 
met  with  in  the  mine.  The  ore  contains  a  great  deal  of  fragmental  material, 
the  major  portion  of  which  is  quartz.  There  is  some  crystalline  quartz 
between  the  fragmental  grains  and  a  large  quantity  of  some  carbonate,  a 
considerable  proportion  of  which  is  in  little  rhombohedra.     This  carbonate 


428  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

is  fresh  and  there  is  no  evidence  that  it  is  changing  into  ore.  It  is  jDrobably 
an  infiltration.  The  Cundy  ore  thus  appears  to  be  a  fragmental  rock  that 
has  been  greatly  enriched  by  iron  oxides.  West  of  the  Foote  shaft  of  the 
mine  the  ore-bearing  beds  are  exposed  in  an  open  pit.  Here  they  are 
even-bedded  quartzites  or  fragmental-looking  jaspers  and  ores  dipping 
about  70°  S.  The  quartzite  or  jasper  is  in  places  richly  ferruginous. 
The  ore  is  in  thin  layers  which  get  thicker  toward  the  north.  Joint  cracks 
intersect  the  rocks  at  right  angles  to  their  bedding,  and  many  of  them  are 
occupied  by  quartz  veins.  At  the  present  time  developments  in  the  mine 
have  not  progressed  far  enough  to  show  the  relations  of  the  ore  body  to  the 
adjacent  rocks. 

The  Vivian  mine  has  but  recently  been  opened  up.  Its  three  shafts 
occupy  the  southeast  quarter  of  the  southwest  quarter  of  sec.  34.  One  of 
them  apparently  obtains  ore  from  the  basal  layers  of  the  Lake  Superior 
sandstone,  and  the  others  from  synclinal  portions  of  the  Traders  jaspilite 
neai"  the  contact  of  this  member  with  the  overlying  Brier  slates. 

NORWAY    AND   CYCLOPS   MINES. 

Anothcn-  exceedingly  important  ore-producing  center  is  Norway,  about  4 
miles  east  of  Quinnesec,  where  the  Norway,  Cyclops,  and  A-ragon  miiies  are 
situated  (PI.  XXXI).  In  this  neighborhood  there  is  undoubted  evidence  of 
the  presence  of  two  westward-pitching  synclines  in  the  dolomite,  within  the 
northern  of  which  the  Norway  mine  is  located  and  within  the  southern  one 
the  Aragon  mine.  The  northern  syncline  is  the  broader,  but  it  is  shallower 
than  the  southern  one  (see  pp.  240-245) ;  hence  it  is  in  the  latter  that  the  best 
developed  ore  deposit  occurs.  The  geological  structure  of  this  area  is 
difficult  to  detei'mine  because  of  close  folding,  brecciation  of  the  slates 
and  jaspilites  involved  in  the  folds,  and  the  lack  of  exposures  at  critical 
localities.  Moreover,  sandstone  covers  the  hill  to  the  west  and  northwest 
of  the  mines  and  prevents  the  tracing  of  the  folds  in  that  direction.  The 
structure  of  the  area  occupied  by  the  Aragon  mine,  the  northeast  quarter 
of  the  northeast  quarter  of  sec.  8,  and  northwest  quarter  of  the  northwest 
quarter  of  sec.  9,  T.  39  N.,  R.  30  W.,  is  fairly  well  known  from  the  under- 
ground workings  of  this  mine.  All  three  members  of  the  Vulcan  formation 
exist  with  their  average  thickness.  They  occur  in  a  rather  sharply  com- 
pressed syncline,  pitching  a  little  north  of  west  at  an  angle  of  about  45° 
and  dipping  a  little  east  of  south  at  an  angle  approximating  60°.  On  this 
are  superimposed  several  smaller  folds,  dipping  and  pitching  in  approxi- 


U    S- GEOLOGICAL   SURVEY 


MONOGRAPH   XLVI     PL. XXXI 


LEGEND 
CAMBRIAN 


OEOLOdlC   MAP  OF  NORWAY  AND  ARAGON   FOLDS  AND  VICINITV,  MICHIGAN 

PAHTS    OF    SECS.  4,  5,a,  AKI)  S),  T.  .'(9  N.,  R.29  W. 

BV  W.  S-  BAYLEv 
J9<)3 


FOR  SECTIONS  SEE  PLATE  XXX f I 


Scale 

^00 


ALGONKIAN.  THE  ORE  DEPOSITS.  429 

mately  the  same  directions.  These  folds  are  overturned  to  the  nortli,  so 
that  the  north  sides  of  the  intervening  anticlines  are  either  vertical  or  dip 
high  to  the  south. 

The  structure  within  the  Norway  fold  is  so  very  obscure,  for  the 
reasons  above  mentioned,  that  it  is  only  with  the  greatest  hesitation  that 
any  explanation  of  it  is  hazarded.  The  three  members  of  the  Vulcan 
formation  have  been  traced  northwest  from  the  Aragon  mine  about  one-half 
mile  by  the  aid  of  drill  holes,  pits,  and  exploring  shafts,  and  the  two  lower 
members  have  been  followed  over  one-fourth  mile  by  the  lower  workings 
of  the  Aragon  mine.  Near  the  quarter  post  between  sees.  5  and  8  the 
Traders  member  appears  to  turn  suddenly  to  the  northeast  and  to  extend 
in  this  direction  at  least  as  far  as  a  point  south  of  the  main  shaft  of  the 
Norway  mine,  which  is  nearly  due  north  of  the  principal  workings  of  the 
Aragon  mine.  They  are  traceable  through  this  distance  by  the  shafts  and 
open  pits  of  the  Cyclops  mine.  Beyond  the  Norway  shaft  the  iron-bearing 
beds  have  not  been  seen,  but  it  is  supposed  that  they  join  the  northernmost 
belt  of  the  Traders  member  somewhere  within  the  Perkins  pit.  From  this 
pit  the  belt  runs  a  little  north  of  west  through  this  and  the  Norway  pit 
until  it  is  lost  under  a  tliick  covering  of  sandstone  near  the  center  of  the 
section.  From  the  point  where  the  belt  makes  the  sharp  turn  to  the  north- 
east there  is  a  prolongation  of  the  iron-bearing  beds  to  the  northwest  for 
a  distance  of  about  1,250  feet.  Here  they  are  apparently  terminated  by 
Brier  slates,  though  the  evidence  of  this  is  very  scanty.  In  this  prolongation 
the  belt  is  about  double  its  normal  width  and  incloses  an  axis  of  slates. 
Thus  the  iron-bearing  lieds  that  have  been  described  as  Traders  form  a 
Z-shaped  belt  with  a  slight  prolongation  from  the  lower  left-hand  angle  of 
the  Z  parallel  to  the  upper  and  lower  lines.  Beyond  the  points  mentioned 
as  the  western  termini  of  the  belts  on  the  surface  nothing  practically 
is  known  about  their  further  extension.  The  country  to  tlie  west  is 
covered  with  a  layer  of  sandstone  which  only  a  few  test  pits  have  pene- 
trated. On  the  west  line  of  the  section  there  is  a  shaft  in  iron  formation 
material,  but  there  is  nothing  between  this  shaft  and  the  Norway  pit  to 
indicate  whether  this  is  an  extension  of  the  Norway  belt  or  of  the  more 
southerly  Cyclops-Aragon  belt. 

Another  source  of  difficulty  in  the  interpretation  of  the  structure  is  the 
brecciated  character  of  the  rocks  involved  in  the  folding:  and  the  obscure 
character  of  their  contacts.     In  nearly  all  the  pits  of  the  Cyclops  and  the 


430  THE  ]MEN0:MINEE  IRON-BEARING  DISTRICT. 

Norway  mines  the  slates  and  jaspilites  are  severely  shattered  and  brecciated. 
Into  the  crushed  slates  ferruginous  material  has  penetrated  to  such  an  extent 
that  in  some  instances  they  have  been  wrought  as  ore.  At  the  Norway  and 
the  Cyclops  pits  faulting  has  unquestionably  accompanied  the  brecciation, 
so  that  the  ore-bearing  beds  in  some  places  appear  to  be  above  a  slate, 
whereas  the  same  beds  apparently  underlie  the  same  slate  in  other  places. 
On  the  east  side  of  Barbara's  pit  (see  map,  PI.  XXXI),  for  instance,  the  iron- 
bearing  beds  are  apparently  under  the  slates  in  an  anticline  pitching  east, 
while  at  the  west  end  of  the  same  pit  they  are  apparenth*  over  the  slates  with 
reibungsbreccia  between  them.  To  the  south  the  jaspilites  may  be  traced 
almost  without  break  into  Green's  pit,  where  they  are  much  brecciated,  and 
on  the  south  side  of  this  pit  they  dip  south  at  a  high  angle  (about  80°)  beneath 
even-bedded,  red  slates.  Traced  west  they  again  appear  in  pit  No.  1,  where 
they  constitute  a  sharp  syncline  underlain  by  a  slate  which  on  the  north  side 
is  severely  brecciated,  and  still  farther  west  on  the  west  face  of  pit  No.  2  they 
are  in  a  distinct,  nearly  symmetrical  syncline  underlain  by  slates  that  are 
not  brecciated  or  which  are  brecciated  only  to  a  very  slight  extent. 

There  is  little  opportunity  for  comparing  the  normal  characters  of  the 
different  slates  with  each  other,  principally  because  of  the  severe  breccia- 
tion and  the  attendant  alteration  to  which  the  rocks  have  been  subjected. 
Cross  sections  of  the  Norway  pit,  however,  seem  to  show  that  the  slates 
south  of  the  ore  deposits  at  this  place  are  in  the  stratigraphical  position  of 
the  Brier  slates,  while  the  drill  holes  on  the  Aragon  property  and  the  under- 
ground workings  of  this  mine  appear  to  prove  that  the  slates  between  the 
Aragon  and  the  Cyclops  ore  beds  are  beneath  the  ore  formation.  On  the 
supposition,  therefore,  that  the  slates  between  the  Norway  and  the  Cyclops 
are  Brier  and  those  between  the  Cyclops  and  Aragon  are  Traders,  or  talcose 
slates  belonging  on  top  of  the  Randville  dolomite,  the  map  and  cross  sections 
shown  on  Pis.  XXXI  and  XXXII  and  fig.  18  have  been '  constructed. 
These  seem  to  explain  the  facts  now  known  as  to  the  distribution  of  the  ore- 
bearing  beds  in  the  three  belts  and  the  relations  of  these  beds  to  the  adjacent 
slates.  It  is  fully  realized,  however,  that  there  may  have  been  a  mistake 
made  in  the  identification  of  the  northern  slates  as  Brier.  The  Norway  ore 
beds  may  be  in  a  compressed  syncline  with  the  slates  to  the  south  in  an 
anticline,  in  which  case  the  structure  as  indicated  on  the  maps  would  have 
to  be  modified  to  this  extent.  There  appears  at  present  to  be  no  way  of 
deciding  this  point. 


U.  S.  GEOLOGICAL  SURVEY 


MONOGRAPH   XLVI      PL.    XXXII 


If 


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Sf^th  level 


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6th  level 

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VERTICAL    NORTH-SOUTH    CROSS    SECTIONS    THROUGH    THE    NORWaY-ARAGON    AREA,    ILLUSTRATING  GEOLOGICAL    STRUCTURE. 

For  positions  of  ses'"*"*.  *oe  map,  P|,  XXXI. 


ALGONKIAN,  THE  ORE  DEPOSITS.  431 

The  explanation  of  the  structure  as  above  outhned  is  to  the  eflPect  that 
the  Norway  belt  is  the  north  side  of  a  syncline  dipping  under  the  slates  to 
the  south  and  rising  on  the  north  side  of  the  Cyclops  belt  in  an  anticline. 
This  antichne  is  confined  to  the  northern  part  of  the  Cyclops  belt,  its  south- 
ern portion  consisting  of  a  syncline  which  is  overturned  to  the  north  in 
Green's  pit.  In  pit  No.  3  this  syncline  is  uprig];t  and  normal  and  is  sepa- 
rated from  the  anticline  to  the  north  by  a  narrow  belt  of  talcose  slates.  The 
entire  belt  is  supposed  to  terminate  to  the  west  by  pitching  beneath  the 
overlying  Brier  slates. 

South  of  the  Cyclops  belt  the  ore-bearing  beds  span  an  anticline  of 
Traders  slates  and  Randville  dolomite,  its  south  limb  reappearing  again  as 
a  southward-dipping  monocline  at  the  Aragon  mine. 

The  Curry  member  has  been  excluded  from  consideration  in  the  above 
discussion,  because  no  inkling  of  the  course  of  the  belt  has  been  obtained 
beyond  the  pits  1,000  feet  west  of  the  quarter  post  between  sections  6  and 
8.  According  to  the  view  outlined  above,  this  member  must  turn  to  the 
northeast  around  the  west  end  of  the  Cyclops  belt  of  the  Traders  beds, 
make  a  reentrant  to  the  east,  and  then  turn  sharply  to  the  west  and  extend 
into  section  6. 

The  distribution  of  the  ore  deposits  in  this  area  confirms  beautifully 
the  generalizations  of  a  former  paragraph  in  which  the  manner  of  occur- 
rence of  the  ore  is  discussed.  At  the  Norway  mine  a  pitching,  shallow 
trouffh  is  being-  mined  for  ore.  It  is  bounded  on  both  the  north  and  the 
south  by  dolomite.  The  fold  is  so  important  as  to  bring  the  dolomite  very 
near  the  surface  (see  sections  on  PI.  XXXII  and  figs.  18,  19).  Between  the 
dolomite  and  the  ore  is  a  certain  amount  of  ferruginous  and  siliceous  slate, 
which,  until  the  demands  for  low-grade,  nonphosphoric  ores  arose,  could 
not  be  mined.  During  the  summer  of  1900,  however,  a  large  amount  of 
this  lean  material  was  shipped. 

In  the  Cyclops  belt  are  several  large  pits,  from  which,  in  all,  some 
286,000  tons  of  ore  had  been  raised  prior  to  1892.  Since  this  date  only  an 
inconsiderable  quantity  has  been  mined.  Practically  all  of  this  ore  came 
from  the  southern  half  of  the  belt,  in  which  the  structure  is  synclinal.  At  the 
southwest  end  of  the  Cyclops  belt,  where  it  turns  southeastward  toward  the 
Aragon  mine,  no  ore  has  been  discovered,  though  the  jaspilites  are  crushed 
into  very  distinct  breccias.  The  structure  at  this  place  is,  of  course, 
anticlinal. 


432 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 


ARAGON    MINE. 


The  Aragou  mine  gives,  jjerhaps,  the  clearest  illustration  furnished  by 
the  district  of  the  principle  of  the  formation  of  ore  in  pitching  troughs  on 
impervious  basements.  Just  east  of  the  Aragou  mine  is  a  sharp  embay- 
ment  in  the  dolomite,  which  may  be  beautifully  seen  above  o-round,  an 
amphitheater  of  limestone  entirely  surrounding  the  low  land  occupied  by 
the  iron-bearing  formation.     A  short  distance   to  the  west  of  this  embay- 


%No  3  SHAFT 


•  No  2  SHAFT 


Fig.  39. — Horizontal  section  of  the  Aragon  mine  at  the  first  level.     One  inch=260  feet. 

ment  the  Aragon  body  was  discovered.  Where  first  found  it  was  at  the 
top  of  the  Traders  member  of  the  ore  formation,  just  below  the  bottom 
of  the  Brier  slate  (see  fig.  39).  At  this  time  no  one  could  have  predicted 
that  this  ore  body  is  really  related  to  the  impervious  talc-schists  of  the 
dolomite  below.  However,  as  mining  continued,  the  ore  deposit  gradually 
and  in-egularly  widened,  and  at  the  fifth  level  assumed  definite  relations 


ALGONKIAN,  THE  ORE  DEPOSITS. 


433 


to  the  dolomite.  From  the  fifth  level  downward  (tigs.  20,  21,  and  40)  this 
relation  has  continued,  the  main  mass  of  the  ore  body  being  found  at  the 
apex  of  the  trough,  and  long  arms  of  ore  extending  up  along  both  limbs  of 
the  fold,  but  especially  along  the  main  dolomite  wall  to  the  north  (see  fig. 
40).  This  occurrence  is  especially  interesting  since  the  ore  deposit  was 
found  steadily  to  increase  in  size  as  it  assumed  definite  relations  to  the 


Fig.  40. — Horizontal  section  of  the  Aragon  mine  at  the  eighth  level. 

underlying  pitching  trough  (fig  41).  At  the  high  levels,  where  it  did  not 
have  an  impervious  basement  furnished  by  the  dolomite  formation,  it  was 
comparatively  small.  As  soon  as  it  had  assumed,  at  lower  levels,  definite 
relations  to  the  dolomite  trough  it  became  a  large  ore  body,  and  has 
continued  to  increase  in  size  to  the  present  depth  now  reached  at  the  eighth 
and  ninth  levels,  where  the  relations  of  the  ore  to  the  j^itching  trough  are 
perfectly  illustrated. 


MON    XLVI — 04r- 


-28 


434 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


Mines  East  of  Aragon  Mine. 

East  of  the  Aragon  mine  there  are  found  in  rapid  succession  the  mines 
of  the  Penn  Iron  Mining  Company,  viz,  the  Curry  and  the  various  shafts 
of  the  AVest  Yulcau,  Central  Vulcan,  and  East  Vulcan  mines.  East  of 
these  again  is  the  A^erona  mine.  Beyond  this  there  are  no  mines  that  are 
active  at  present,  although  at  the  extreme  east  end  of  the  district  are  the 
abandoned  pits  of  the  oldest  of  all  the  Menominee  mines — the  Breen  and 
the  Emmett.  Except  at  the  last  two  mentioned  mines,  at  the  AVest  A^ulcan 
and  at  the  western  shafts  of  the  East  A^ulcan  mine,  the  geological  relations 
of  the  different  members  of  the  A^iilcan  formation  with  one  another  appear 
to  be  simple,  and  the  ore  deposits  are  apparently'  contact  deposits. 


Scale 

200 


^/•rfrfeSEjgjgrr       '    X 


Fig.  41. — Vertical  east-west  longitudinal  section  of  the  Aragon  mine,  nortli  fold. 

At  the  AVest  A^ulcan  and  the  eastern  shafts  of  the  East  A-^ulcan  mine 
folds  exist  in  the  Cuny  member  at  least,  and  these  have  determined  to 
some  measure  the  deposits  in  this  member.  From  these  shafts  and  that  of 
the  Curry  mine  ore  is  raised  from  the  Curry  member  as  well  as  from  the 
Traders  beds,  and  at  the  East  A^ulcan  shaft  No.  3  the  ore  has  come 
exclusively  from  the  Curry  beds. 

BKIER   HILL   AND   CURRY   MINES. 

The  Brier  Hill  explorations  occupy  the  southeast  quarter  of  the  north- 
west quarter  of  sec.  9,  T.  39  N.,  R.  29  AV.,  which  is  immediately  east  of 
the  Aragon  location.     East  of  this,  in  the  southwest  quarter  of  the  north- 


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0 

Noiivwaoj  NV3nn/\ 


ALGONKIAN,  THE  ORE  DEPOSITS. 


435 


a' 


east  quarter  of  the  same  section,  is  the  Curry  mine  (PL  XXXIII).     The 
Brier  Hill  mine  was  abandoned  after  yielding   14,981  tons  ji 

of  ore.     The  Curry  mine  is  still  an  important  producer.  |=      | 

To  the  east  of  the  Aragon  mine  the  three  members  of 
the  Traders  formation  can  be  traced  almost  continuousl}'  by 
surface  exposures,  test  pits,  and  mine  workings  to  the  east  side 
of  the  Curry  location.  For  most  of  this  distance  they  follow 
a  uniform  direction  of  about  15°  south  of  east  without  notable 
variations  in  thickness.  To  the  north  are  splendid  exposures 
of  the  Randville  dolomite  (see  p.  267),  and  to  the  south  is 
the  Hanbury  slate,  which  has  been  developed  at  a  number 
of  places  by  the  drifts  and  crosscuts  from  exploring  shafts- 
Between  the  Brier  Hill  and  the  Aragon  mines  there  is  an 
excellent  section  exhibited  on  the  surface  from  the  bottom  of 
the  Traders  member  to  the  top  of  the  Brier  slate,  and  near  by 
a  crosscut  from  the  Brier  Hill  exploring  shaft  extends  the 
entire  width  of  the  Curry  member.  The  approximate  widths 
of  the  several  belts  on  the  surface  are:  Traders  member,  150 
feet;  Brier  slate,  350  feet;  Curry  member,  225  feet;  or  a  total 
of  725  feet.  The  dip  of  the  beds  in  the  north — i.  e.,  at  the 
base  of  the  formation — is  only  20°  S.  This  increases  gradu- 
ally to  the  south,  the  dip  of  the  beds  at  the  top  of  the  Brier 
slate  being  as  high  as  80°  S.  The  thickness  of  the  members 
calculated  from  their  widths  and  dips  is:  Traders,  60  feet; 
Brier,  338  feet;  Curry,  220  feet;  making  a  total  thickness  of 
618  feet.  A  section  across  these  beds  is  shown  in  fig.  42.  To 
the  north,  at  the  base  of  the  little  cliff  overlooking  the  swamp 
that  stretches  to  the  dolomite  cliffs  about  300  feet  still  farther 
north,  are  a  few  layers  of  a  light-colored  slate,  with  which  are 
interleaved  a  few  thin  beds  of  quartzite.  Above  these  and 
forming  the  main  portion  of  the  face  of  the  little  cliff  is  a 
3-foot  bed  of  quartzite  conglomerate,  and  above  this  a  series 
of  beds  consisting  of  layers  of  conglomerate,  slates  like  those 
at  the  base  of  the  cliff,  and  thin  beds  of  specular  mottled  ore. 
The  conglomerates  are  fairly  coarse-grained  quartzites,  inclos- 
ing fragments  of  jasper,  ore,  and  quartz.  These  constitute 
the  principal  portion  of  the  series,  the  slates  and  ores  being  in  thin  beds 


436  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

and  iu  greatly  subordinate  quantity.     Following  these  to  the  south  is  a 
series  of  bedded  jaspilites  about  75  feet  wide,  and  south  of  these  is  a  wide 
baud  of  Brier  slates  showing  beautiful  bedding  bands  in  their  weathered 
surfaces.     To  the  north,  at  the  base  of  the  series,  they  are  very  jaspery  and 
quartzose,  but  higher  up  the  propoi-tion  of  siliceous  matter  diminishes  and 
the  slates  become  t3i:)ically  developed.     The  Curry  ore-bearing  beds  are 
not  exposed  on  the  svn-face  at  this  place,  but  farther  east,  at  the  open  pit 
of  the  Curry  mine,  they  are  well  shown.     Here  the  slates  grade  into  the 
jaspihtes  by  interlaminations  of  slaty  and  siliceous  materials  (see  p.  351). 
Just  east  of  the  little  ridge  composed  of  the  quartzite-conglomerates  is  a 
pit,  on  the  dump  of  which  are  dark-gray  slates  with  all  the  microscopical 
characteristics  of  the  Hanbury  slate,  and  a  few  paces  south  of  this  is  a  small 
ledge  of  a  dark,  serpentinous-looking  rock  that  apparently  contains  small 
fragments  of  ore  and  jasper.     It  is  cut  by  irregular  veinlets  of  calcite. 
Under  the  microscope  serpentine  is  seen  to,  constitute  a  large  portion  of 
the  rock.     It  is  airanged  in  such  a  way  as  to  suggest  the  flowage  struc- 
ture in  lavas.     The  rock  is  probably  a  breccia  on  the  contact  of  the  dolo- 
mite and  the  Traders  beds  like  that  so  well  developed  in  the  Norway  pit 
and  in  the  open  pits  of  the  Curry  mine.     The  slate  is  more  difficult  to 
explain.     The  pit  from  which  it  was  taken  is  north  of  the  breccia  ledge. 
Of  course  the  relations  of  the  slate  to  the  serpentinous  breccia  and  to 
the  Traders  slates  are  not  known,  since  the  rock  has  been  seen  only  on 
the  dump  pile  of  the  pit.     Two  explanations  suggest  themselves  to  account 
for  the  presence  of  the  slate  in  this  place.     Either  one  is  plausible.     The 
first  is  that  the  slate  is  one  of  the  lower  beds  of  the  Traders  member, 
in  which  case  the  boundary  of  the  Vulcan  formation  on  the  map  should 
be  placed  a  little  farther  north,  with  the  breccia  an  inlier  of  the  Raud- 
ville  formation,  suiTOunded   by  Traders    beds.     The   second    explanation 
accounts  for  the  presence  of  the  slate  at  this  place  on  the  supposition  that  it 
is  a  small  remnant  of  Hanbury  slate,  overlapped  beyond  the  Traders  beds 
and  preserved  from  erosion  by  its  position  in  the  lowlands  of  the'  swamp. 
East  of  the  Brier  Hill  mine  the  dolomite  and  the  Traders  beds  are  very 
close  together,  the  Traders  layer  nearest  the  dolomite  being  a  coarse-grained 
quartzite  conglomerate.     This  has  already  been  described  on  a  preceding 
page  (p.  271). 

The  position  of  the  ore  deposit  in  the  Brier  Hill  mine  is  not  known, 


ALGONKIAN,  THE  ORE  DEPOSITS.  437 

but  judging  from  the  structural  relationships  of  the  various  rocks  in  its 
vicinity  the  deposit  must  be  on  or  near  the  contact  of  the  Traders  member 
with  the  underlying  dolomite,  which  on  the  surface,  near  the  shaft,  dips 
about  50°  S. 

The  Curry  location  is  immediately  west  of  the  Brier  Hill  mine.  The 
iron-bearing  formation  continues  from  the  Brier  Hill  mine  eastward  in  a 
uniform  direction  to  the  open  pits  of  the  Curr}'  mine,  where  the  Traders 
member  departs  sharply  from  this  direction,  its  northern  boundary  making 
a  deflection  to  the  north,  forming  an  embayment  in  the  Randville  dolomite. 
The  extent  of  this  deflection  is  not  accurately  known  because  the  Huronian 
rocks  are  covered  with  a  fairly  thick  deposit  of  the  Lake  Superior  sandstone. 
This,  however,  has  been  penetrated  at  a  number  of  jilaces,  uncovering  the 
underlying  Traders  beds  dipping  south  at  45°.  West  of  the  northward  turn 
the  jaspilites  of  this  member  are  exposed  in  a  little  hillock  with  all  the  features 
of  typical  phases  of  these  rocks  (see  pp.  273-277).  Indeed,  the  jaspers 
interbanded  with  the  ore  layers  are  so  similar  to  the  typical  jaspers  of  the 
Negaunee  formation  in  the  Marquette  district  that  for  some  time  the  beds 
were  supposed  to  be  of  Negaunee  age.  These  rocks  strike  N.  80°  to  85°  W. 
and  dip  60°  to  82°  S.  East  of  this  exposure  the  Traders  beds  make  their 
northward  turn,  and  at  this  point  there  are  several  large  open  pits  which 
well  display  both  the  jaspilites  and  the  Brier  slates.  These  pits  mark  the 
southern  boundary  of  the  Traders  belt,  which  is  continued  eastward 
through  the  West  Vulcan  property  by  another  series  of  equally  large 
pits.  In  the  western  pits,  those  on  the  Curry  location,  the  jaspilites  are 
folded  into  a  number  of  small  synclines  and  anticlines  pitching  south- 
east at  low  angles.  Near  the  contacts  with  the  overlying  Brier  slate 
slipping  has  taken  place.  The  jaspilites  are  profoundly  brecciated,  the 
cement  between  the  fragments  of  the  breccia  oftentimes  being  an  ore  which 
is  now  schistose  and  specular.  It  was  from  this  brecciated  zone  that  the 
ore  was  removed  in  earlier  days.  Pit  No.  3  (see  map,  PI.  XXXIII)  exhibits 
the  relations  of  the  rocks  in  a  very  beautiful  manner.  A  sketch  of  its  plan 
is  shown  in  fig.  43.  At  the  northwest  corner  of  the  pit  is  a  little  syncline 
in  interbanded  flinty  jaspers  and  specular  layers  pitching  about  20°  SE. 
Superposed  on  this  are  several  minor  rolls.  Above  this  is  a  conglomerate 
or  breccia,  composed  of  fragments  of  ore  and  jasper  cemented  together  by 
a  sandy  matrix  which  is  not  unlike  the  material  of  the  Brier  slates  on  the 


438 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


east  side  of  the  pit.  The  conglomerate  is  not  more  than  3  or  4  feet  thick. 
It  is  overlain  by  banded  slates  and  frag-mental-looking  jasper  and  ore 
layers.  A  little  farther  east,  on  the  north  side  of  the  pit,  the  jaspilites  are 
well  bedded.  Large  lenses  of  jasper  occur  in  them  and  in  many  places  the 
series  appears  to  be  brecciated.  Above  the  jaspilites  are  the  Brier  slates  at 
the  northeast  comer  of  the  pit.  The  former  rocks  are  brecciated  and 
between  them  and  the  overlying  slates  is  a  deposit  of  ore.  That  portion 
of  the  series  here  exposed  measures  not  more  than  45  feet  in  thickness_ 

The  most  distinct  breccia  is  at  the  top 
of  the  Traders  member  near  its  con- 
tact with  the  slate.  It  is  this  breccia 
that  furnished  the  ore  that  was  for- 
merly mined  at  this  place.  Several 
other  synclines  and  anticlines  are  indi- 
cated in  the  sketch.  PI.  XXII,  A  is  a 
reproduction  of  a  photograph  of  the 
upper  surface  of  the  southernmost 
anticline.  This  shows  a  breccia  which 
has  been  sheared  until  it  simulates  a 
conglomerate.  It  is  now  composed  of 
large  lenses  of  jasper  in  a  matrix  of 
beautifully  schistose  ore.  The  jasper 
lenses  are  coated  with  ore,  so  that 
they  do  not  stand  out  clearly  in  the 
reproduction.  Their  positions,  how- 
ever, can  be  recognized  by  the  dif- 
ferences in  the  reflections  from  the 
glistening  surface.  A  little  to  the  northwest  of  jait  No.  3  a  small  excava- 
tion in  sandstone  has  uncovered  the  underlying  jaspilites,  which  at  this 
place  are  very  flat  lying.  Thus  the  larger  fold  in  the  iron  formation  in  the 
north  portion  of  the  Curry  and  West  Vulcan  locations  is  accompanied  by 
minor  folding  in  pit  No.  3,  which  may  be  regarded  as  being  situated  on  a 
flat  anticline  pitching  at  a  low  angle  to  the  southeast.  The  gentle  character 
of  the  major  folding  is  likewise  indicated  by  the  gentle  minor  folds  exhib- 
ited in  the  pit.  Along  the  contact  of  the  iron  formation  with  the  overlying 
slates  movement  took  place,   and  this  was  accompanied  by  brecciation, 


20  fe.et 


Fig.  43. — Plan  of  No.  3  pit,  Curry  mine,  and  section  along 
its  north  end. 


U    S    GEOLOGICAL    SURVEY 


MONOGRAPH    XLVI       PLXXXIV 


Gl-;()I,OC.IC  MAP  OK 
FRAL-  MILCWN  AND  PORTION  OF  WEST  VULC.VN  ARE  AS.MU  11 1(  JAX 

S.ViSKC.  10. T  ;i!l  N..H.  2!)\ST 
BVWS.BA1  l.i:-!- 


Base  of  this  map  furnished  by  Penniron  Mining  Company 


ALGONKIAN,  THE  ORE  DEPOSITS.  439 

which  affected  not  only  the  jaspilites,  but  also  to  some  extent  the  overlying 
slates.  The  latter,  where  not  brecciated  as  a  whole,  contain  bands  of 
brecciated  material.  Where  brecciation  occurred  the  slates  are  traversed 
by  quartz  veins  and  the  jaspilites  are  ferruginized. 

South  of  the  Traders  beds  the  Brier  slates  and  the  Curry  member  are 
exposed  in  pits  and  tunnels  which  furnish  an  almost  uninterrui^ted  section 
from  the  bottom  of  the  former  to  the  top  of  the  latter.  The  gradation 
between  the  two  members  as  exhibited  at  tliis  place  has  alreadj'  been 
described  in  preceding  pages  (pp.  350-351),  and  the  fact  that  both  the 
slates  and  the  ores  are  characterized  by  the  presence  of  an  abundance  of 
dolomite,  which  not  only  saturates  the  rocks  and  constitutes  a  matrix  in 
which  the  other  components  lie,  but  also  cuts  the  Curry  beds  in  veins, 
has  been  likewise  sufficiently  emphasized  (pp.  339  and  347). 

The  ore  of  the  Curry  mine  comes  largely  from  the  Curry  beds.  The 
exact  method  of  occurrence  of  the  ore  deposit  in  this  case  is  not  known. 
There  appears  to  be  no  fold  here,  but  the  ores  are  so  shattered  that  it  is 
possible  that  there  was  movement  along  the  contacts  of  the  Curry  with  the 
Brier  member  and  that  the  ores  are  the  result  of  the  ensuing  brecciation, 
just  as  they  are  in  the  case  of  the  pits  to  the  north.  In  any  event  the  ore 
deposit  is  apparently  along  the  contact  with  the  underlying  slate,  which  at 
this  place  dips  about  75°  S. 

WEST    VULCAN    MINE. 

The  West  Vulcan  location  occupies  the  southeast  quarter  of  the  north- 
east quar'  i-  of  sec.  9,  and  the  southwest  quarter  of  the  northwest  quarter 
and  the  jiorthwest  quarter  of  the  southwest  quarter  of  sec.  10,  T.  39  N., 
R.  29  W.  The  principal  shafts  now  working  are  C  shaft  and  No.  2  in  sec. 
9  and  the  Klondike  shaft  in  sec.  10.     (See  Pis.  XXXIII  and  XXXIV.) 

The  three  members  of  the  Vulcan  formation  can  be  followed  uninter- 
ruptedly across  the  West  Vulcan  locations  by  means  of  exposures,  test  pits, 
and  shafts.  Exposures  are  not  as  common  in  the  eastern  half  of  the  area 
as  they  are  in  its  western  half,  and  test  pitting  is  not  as  uniformly  distrib- 
uted. There  is  abundant  evidence,  however,  to  show  tliat  the  Traders 
member  resumes  its  normal  thickness  and  direction  at  the  line  between 
sees.  9  and  10  and  continues  in  a  straight  course  across  the  western 
portion  of  the  last-named  section.  Tlie  greatest  width  of  the  member  in 
sec.  9   is  about   650  feet.     This  is  due  to    the   fold   referred    to    in    the 


440  THE  MENOMINEE  IRON -BEARING  DISTRICT. 

descriptions  of  the  geolog-y  of  the  Curry  mine.  The  southern  boundary 
of  the  belt  is  marked  by  the  large  open  pits  already  mentioned  and  a  group 
of  small  pits  that  penetrate  the  sandstone.  Its  northern  boundary  is  not 
definitely  known.  A  drill  hole  situated  near  the  northern  limit  of  the 
southeast  quarter  of  the  northeast  quarter  of  sec.  9,  put  down  at  an  angle 
of  35°  N.,  after  passing  through  300  feet  of  sandstone,  penetrated  56  feet 
of  "ore  and  jasper"  into  dolomite.  A  little  group  of  pits  to  the  southwest 
of  this  drill  hole  have  uncovered  jaspilites  with  an  average  dip  of  45°  S. 
At  the  base  of  the  sandstone  is  a  layer  of  conglomerate  composed  in  large 
part  of  bowlders  of  ore  and  jasper. 

In  the  large  pits  on  the  southern  side  of  the  belt  the  relations  of  the 
rocks  are,  in  the  main,  much  the  same  as  those  in  the  pits  to  the  west.  Dis- 
tinct folds  are,  however,  absent,  though  slight  corrugations  are  noted  in 
the  jaspilites.  This  is  to  be  expected,  since  the  large  fold  is  not  as  sliarp  at 
this  place  as  it  is  to  the  west,  and  therefore  disturbances  in  the  bedding  are 
less  marked.  Just  west  of  pit  No.  2  the  strain  was  relieved  by  a  slight 
fault  between  the  jaspilites  and  the  Brier  slates.  The  jaspilites  in  these 
pits  are  low  dipping,  35°  to  55°  S.,  and  they  are  fractured  into  frag- 
ments forming  distinct  breccias.  As  was  the  case  in  the  pits  to  the  west, 
these  breccias  furnished  a  large  quantity  of  ore  that  was  mined  from 
the  surface.  The  south  sides  of  the  pits  mark  the  contact  between  the 
Traders  member  and  the  Brier  slate.  A  few  hundred  feet  west  the  slate 
can  be  seen  to  make  a  slight  erabayment  north  into  the  Traders  beds, 
indicating  the  presence  of  a  small  fold  conforming  to  the  larger  one  in  the 
jaspilites.  South  of  the  open  pits,  however,  it  resumes  its  normal  direction, 
but  with  a  little  greater  width  than  normal  because  of  the  diminution  in 
the  angle  of  dip,  which  here  is  only  50°  to  65°  S.  Farther  south  the  dip 
increases,  until  at  the  south  border  of  the  slate  belt  it  reaches  85°  S. 
Tunnels  and  pits  afford  a  nearly  complete  section  across  the  slate  member, 
which  is  not  essentially  different  from  the  section  at  the  Curry  mine.  The 
dips  of  the  slate  vary  from  place  to  place,  as  indicated  on  a  former  page 
(see  fig.  26,  p.  358).  In  the  large,  open  pit  of  shaft  No.  1  the  Curry  member 
is  well  exposed. 

In  that  portion  of  the  West  Vulcan  location  east  of  the  section  line 
between  sees.  9  and  10,  as  has  been  stated,  there  are  few  exposures.  In 
the  open  pit  at  shaft  No.  1  the  Curr}-  beds  can  be  seen  dipping  south  at 


ALGONKIAN,  THE  ORE  DEPOSITS. 


441 


high  angles.  North  of  the  jaspihtes  are  the  Brier  slates  bordering  the  north 
side  of  the  pit  and  forming  an  exposure  along  the  railroad  track,  on  its 
north  side,  in  which  the  strike  and  dip  of  the  slates  are  well  sliown.  The 
rocks  are  of  the  normal  tyjje,  somewhat  weathered  and  stained  brown  by 
limonite.  They  strike  N.  70°  W.  and  dip  65°  S.  at  the  east  end  of  the 
exposure  and  85°  S.  at  the  west  end.  South  of  the  jaspilites,  in  some 
places  forming  the  south  side  of  the  pit,  gray  slates  are  exposed.  These, 
in  many  places,  ai'e  graphitic,  and  on  the  contact  with  the  jaspilites  are 
much  sheared.  Small  crumplings  are  noted  at  many  places,  especially 
where  the  shearing  is  marked.  On  the  east  side  of  the  pit  a  narrow  band 
of  a  greenish  decomjjosed  rock  lies  between  the  slates  and  the  jaspilites. 
Sections  of  this  rock  under  the  microscope  show  slight  evidences  of  being 


Fig.  44. — Horizontal  section  of  the  West  Vulcan  mine  at  the  eighth  level. 

igneous  in  the  presence  of  masses  of  secondary  products  that  may  have 
been  derived  from  feldspars.  The  rock  is  probably  a  basic  dike  that  cuts 
between  the  jaspilites  and  slates.  It  is  the  best  example  of  a  dike  in  the 
iron-bearing  series  within  the  district.  Igneous  intrusions  within  the 
Hanbury  slate  area  are  quite  common,  but  intrusions  into  the  Viilcan  series 
are  extremely  rare. 

All  the  other  pits  in  this  sixteenth  of  a  section  are  small.  Individually 
they  exhibit  no  features  that  throw  light  on  the  relations  of  the  rocks  to 
one  another.  Their  distribution,  however,  is  such  as  to  develop  beyond 
question  the  existence  of  a  fold  in  the  Brier  slates,  the  Cuny  beds,  and  the 
overlying  Hanbury  slates,  as  indicated  on  the  map.  The  fold  is  shar})  and 
somewhat  compressed.     Along  its  north  limb  the  Curry  member  is  only  50 


442 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


feet  wide,  whereas  farther  west,  where  the  dip  is  approximately  the  same,  its 
width  is  about  175  feet.  If  this  fold  is  the  same  as  that  discovered  on  the 
eighth  level  of  shaft  No.  2  (see  p.  444,  and  fig-.  44),  its  pitch  must  be  about 
40°  W.  Nortli  of  the  north  side  of  the  fold  there  are  no  explorations 
within  less  than  280  feet.  At  this  distance  there  are  two  pits,  and  a  third 
is  situated  100  feet  farther  north.     These  are  all  in  jaspilites,  which  must 


North 
No. 3  SHAFT 


SHAFT 


South 


400  feet 


Fig.  45. — Vertical  north-south  cross  section  through  No.  2  shaft,  West  Vulcan  mine. 

belong  in  the  Traders  member,  the  intervening  space  between  them  and 
the  fold  being  occupied  by  the  Brier  slate,  which  would  have  about  its 
normal  thickness.  North  of  the  northernmost  of  the  pits  just  mentioned, 
and  distant  from  it  about  100  feet,  is  an  isolated  excavation  in  talcose 
slates,  such  as  usually  occur  between  the  Randville  dolomite  and  the  lower- 
most Vulcan  beds.     The  dolomite  must  be  onlv  a  few  feet  to  the  north. 


ALGONKIAN,  THE  ORE  DEPOSITS. 


443 


The  country,  however,  is  covered  by  the  Cambrian  sandstone,  which  con- 
stitutes an  effectual  obstacle  to  any  attempts  to  map  the  areal  distribution 
of  the  Huronian  formations  in  the  absence  of  test  pits. 


••BURNT'  SHAFT 


5th  level  '/• 


6th  leuel , 


7th  leuel  ',, 

l/i 


8th  level ' 


9th  level  /■ 


70th  level', 


7 1th  level/// 


Uth  levelimMSlT'/i'n/^^r. 


13th  level   M'.' 


40Q  feet 


14th  lem 


istiiiiMiims^j^i^^^'Z^  T 


llmf^m^ 


Fig.  46. — Vertical  north-south  cross  section  through  Burnt  shaft,  West  Vulcan  mine. 


The  ore  of  the  principal  West  Vulcan  shafts  is  obtained  from  both  the 
Traders  and  the  Curry  horizons,  as  shown  in  figs.  45  and  46.     The  ore  of 


444 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


the  lower  horizon  now  being  exploited  occurs  immediately  below  the  Brier 
slates,  at  the  top  of  the  Traders  member.  The  ore  of  the  higher  horizon 
occurs  in  the  Cuny  member  between  the  Brier  slates  and  the  Hanbury  slate, 
extending  from  one  to  the  other  (see  figs.  45  and  4G).  The  three  contacts  of 
the  two  iron-bearing  horizons  witli  the  Brier  and  Hanbury  slates  are  planes 
alouf  which  movement  and  brecciatiou  have  occurred,  and  therefore  where 
percolating  waters  have  been  active.  These  ore  bodies  have  a  considerable 
longitudinal  extent,  but  as  yet  have  not  shown  great  width.      The  southern 


M  stake 


Curry  member 


BURNT  SHAFT 


200  feet 


Fig.  47. — Horizontal  section  of  the  West  Vnlcan  mine  at  twelfth  level. 

deposit  of  the  West  Vulcan  mine  at  shaft  No.  2  shows  very  well  the 
relation  between  sharp  folding,  and  therefore  brecciatiou,  and  differential 
movement  between  the  iron-bearing  member  and  Brier  and  Hanbury  slates. 
Here,  at  the  west  end  of  the  mine,  is  a  very  sharp  fold  in  the  slate  and  iron- 
bearing  member  (see  fig.  44).  This  fold  appears  on  the  surface  to  the  east 
of  the  section  line,  where  it  is  exploited  in  part  by  the  Klondike  shaft. 
From  the  relative  positions  of  the  apex  of  the  syncline  in  the  Hanbury 
slate  at  the  surface  and  on  the  eighth  level  of  shaft  No.  2,  it  is  seen  that  the 


ALGONKIAN,  THE  ORE  DEPOSITS. 


445 


fold  pitches  almost  due  west  at  about  40°.  It  is  probable  that  the  existence 
of  this  fold  in  the  Curry  member  has  a  great  deal  t(i  do  with  the  produc- 
tiveness of  the  formation  at  this  place,  for  when  folding-  is  not  present  the 
Curry  member  is  usually  very  lean. 

The  plan  and  cross  sections  of  the  levels  leading  from  the  "  C  "  shaft 
show  the  same  disposition  of  ore  with  respect  to  the  surrounding  rocks  (see 
figs.  46  and  47)  as  at  shaft  No.  2.  The  irregular  shapes  of  the  ore  bodies  are 
beautifully  shown  on  the  plan  of  the  twelfth  level  (fig.  47)  and  in  the  cross  sec- 


1/1/0.2  SHA/r 


r]  ^T<n<frs  o,^-l,r„^.^^  ^^ 


~^C. 


"fe  ~-^-t~.-- ~ 


I  BURNT  SHAFT 


•^  stake 


''''U  member. . 


300  feet 


Fir.  48.— Horiznntal  section  of  West  Vulcan  mine  at  the  thirteenth  level. 

tion  (figs.  46  and  49).  The  southern  ore  body  appears  at  present  to  be  a 
western  ])itching  lens,  but  additional  work  to  the  east  of  the  cross  section  may 
show  that  the  Curry  beds  at  that  place  have  been  pinched  out  and  that  they 
reappear  again  farther  east.  It  will  be  noted  that  the  Brier  slates  have 
nearly  disappeared,  the  thickness  of  200  feet,  which  separated  the  two  ore 
deposits  in  the  ninth  level,  having  diminished  to  about  30  feet  on  the  thir- 
teenth level.  The  plan  of  the  thirteenth  level  (fig.  48)  seems  to  show  that 
the  east  end  of  the  ore  deposit  which  terminates  on  the  twelfth  level,  250 


446 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


feet  east  of  the  Burnt  shaft,  does  not  extend  to  the  depth  of  the  thirteenth 
level,  its  place  being  taken  by  a  narrow  belt  of  jaspilite.  If  upon  further 
exploration  it  is  found  that  the  Curry  beds  actually  end  at  this  place,  as  the 
ore  deposit  appears  to  do,  or  if  it  is  found  that  they  end  a  little  farther  east, 
their  termination  will  undoubtedly  be  discovered  to  be  due  to  the  little  fold 
already  referred  to  as  exhibited  on  the  surfaces  east  of  shaft  No.  1  and  on 
the  eighth  level  of  shaft  No.  2.  If  this  fold  continued  to  pitch  west  at  the 
same  angle  below  the  eighth  level  as  it  does  between  this  level  and  the 


m 


300  feet 


Fig.  49. — Vertical  north-south  cross  section  through  West  Vulcan  mine,  250  feet  east  of  the  Burnt  shaft.    The  dip  is  to  the 

south. 

surface  its  apex  should  occur  somewhere  near  the  position  of  the  end  of 
the  cross  cut  on  the  thirteenth  level  of  "C"  shaft  (compare  also  fig.  49). 
Fig.  50  is  a  plan  of  the  fifteenth  level  of  the  "  C  "  shaft.  This  is  a  cross- 
cut traversing  the  entire  Vulcan  formation  from  the  talc-schists  underlying 
the  Traders  member  to  the  Hanbury  slates  overlying  the  CuiTy  member. 
The  width  of  the  formation  is  here  300  feet,  of  which  160  feet  is  occupied 
by  the  Traders  member,  125  feet  by  the  Brier  slates,  and  15  feet  by  the 
Curry  beds.  The  narrowness  of  the  Curry  member  may  again  be  due  to 
the  presence  of  the  fold  alluded  to  above. 


ALGONKIAN,  THE  ORE  DEPOSITS: 


447 


At  the  contact  of  the  Curry  jaspihtes  with  the  Hanbury  slates  at  the 
south  end  of  this  crosscut  and  at  the  south  end  of  the  Httle  crosscut 
extending  south  from  the  east  end  of  the  thirteenth  level  is  the  peculiar 
cherty-looking-  rock  which  has  already  been  referred  to  as  differing- 
somewhat  from  anything  else  seen  in  the  district,  with  the  exception  of 
an  apj^arently  similar  rock  found  at  the  end  of  a  drift  from  the  Klondike 
shaft  and  interbedded  in  thin  layers  with  the  jaspilites  on  the  dump  heap 


■aHefi, 


"•ember 


Center  line  of  section 


''''*  "•enber 


^'ate 


Fig.  50.— Horizontal  section  of  West  Vulcan  mine  at  the  fifteenth  level. 

of  this  shaft.  The  West  Vulcan  rock  is  evenly  but  thinly  laminated,  hard, 
dense,  and  gray,  and  is  traversed  by  very  narrow  veins  of  dark-green 
chlorite  along  joint  cracks  and  cut  by  wider  veins  of  calcite  or  dolomite 
and  of  pyrite,  or  by  veins  composed  of  a  mixture  of  the  last-named  mineral 
and  quartz.  Pyrite  is  also  disseminated  through  the  mass  of  the  rock,  in 
some  places  as  minute  granules  so  small  as  to  be  almost  imperceptible  to 
the  unaided  eye;    in  other  places  in  larger  particles  so  thickly  crowded 


448  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

together  as  to  make  the  rock  almost  a  massive  aggregate  of  pyi'ite 
granules.  In  the  latter  case  the  pyrite  also  occurs  in  veins  the  main 
trunks  of  which  run  parallel  to  the  bedding,  and  send  off  minor  branches 
that  anastomose  through  the  rock  in  all  directions.  In  the  specimen 
collected  from  the  dump  of  the  Klondike  shaft  the  cherty  rock  appears 
as  a  layer  between  thin,  dense  ore  layers.  It  contains  very  little  pyrite, 
but  in  place  of  this  mineral  thei  e  are  tiny  veins  of  limonite  and  of  hematite. 
In  some  places  the  chert  passes  into  normal  jasjjer.  In  this  particular  case 
the  light-colored  band  appears  to  be  a  true  chert  belonging  to  the  Curry 
member.  From  the  depths  at  which  the  West  Vulcan  specimens  were 
found,  viz,  1,000  feet  and  1,200  feet  beneath  the  surface,  it  was  at  first 
thought  that  they  might  represent  remnants  of  the  original  rock  that  gave 
rise  to  the  jaspilites.  Upon  examination  in  thin  section,  however,  the  rock 
is  found  to  be  made  up  mainly  of  fragmental  and  cherty  quartz  and  sericite, 
with  the  addition  here  and  there  of  small  fragments  of  plagioclase,  rutile, 
and  possibly  minute  particles  of  zircon.  In  some  sections  these  are  the 
only  constituents,  but  in  many  others  dolomite  is  also  rather  abundant  in 
the  form  of  small  veins  and  nests  disseminated  irregularly  through  the 
mass.  No  crystals  of  this  dolomite  were  observed  in  the  specimens  studied, 
nor  was  any  trace  of  a  nodular  structure  discernible.  The  rocks  are 
plainly  not  original  carbonates,  nor  are  they  representatives  of  original 
pyritiferous  beds  that  may  have  served  as  the  sources  of  the  iron  in  the 
Vulcan  formation.  They  are  presumably  dolomitic  phases  of  the  Haubury 
slates  that  were  silicified  near  the  contact  with  the  Curry  beds  by  the  same 
process  that  silicified  these,  the  pyrite  and  much  of  the  carbonate  being 
subsequent  infiltrations.  The  rock  in  the  drift  at  the  Klondike  shaft  was 
obtained  from  a  depth  of  only  175  feet.  It  differs  from  the  specimens  from 
the  West  Vulcan  levels  in  containing  so  much  carbonate  and  so  little  sec- 
ondary quartz  that  it  niay  be  rightfully  called  a  cherty  dolomite.  In  this 
particular  instance  the  rock  is  minutely  brecciated  and  is  cut  by  both  calcite 
and  chert  veins,  so  that  it  is  difficult  to  determine  exactly  the  proportions 
of  chert  and  carlionate  in  the  original  rock.  It  is  certain,  however,  that  the 
rock  does  not  represent  original  sideritic  beds  from  which  the  ii'on  of  the 
ore  deposits  was  obtained. 


ALGONKIAN,  THE  ORE  DEPOSITS.  449 


CENTRAL    VULCAN    AREA. 


This  area  includes  the  east  half  of  the  southwest  quarter  of  sec.  10 
and  the  entire  southeast  quarter  of  the  same  section.  It  lies  immediately 
east  of  the  West  Vulcan  area  and  occupies  the  whole  stretch  of  the  iron- 
bearing-  belt  between  the  West  Vulcan  and  the  East  Vulcan  mines.  There 
are  no  mines  at  present  operating  in  this  district,  nor  are  there  any  natural 
exposures  of  the  iron-bearing-  rocks.  A  number  of  exploring-  pits  and  a 
few  exploring  shafts,  besides  the  old  open  pit  of  the  Central  Vulcan  mine, 
serve  to  trace  the  Curi-y  belt  about  three-fourths  of  the  way  across  the 
area.  The  Traders  belt  has  been  opened  up  at  only  two  |)oints — by  a 
shaft  indicated  on  the  map  (PI.  XXXIV)  as  Jones's  shaft  and  by  a  crosscut 
from  a  shaft  in  about  the  center  of  the  northeast  quarter  of  tlie  section. 
From  Jones's  shaft  a  drift  extends  south  into  the  Brier  slates.  The  width 
of  the  slate  belt  here  is  about  540  feet,  as  against  about  270  feet  north 
of  the  West  Vulcan  or  Klondike  fold,  and  340  feet  in  the  East  Central 
tunnel,  running  north  from  the  exploring  shaft  in  the  eastern  portion  of 
the  area.  The  excessive  width  of  the  belt  at  Jones's  shaft  is  ascribed  to 
repetition  of  the  beds  by  the  fold  discovered  to  the  west.  This  folding- 
necessitates  the  existence  of  a  corresponding-  fold  in  the  Traders  beds  east 
of  Jones's  shaft  and  a  corresponding  embajnnent  in  the  margin  of  tlie 
dolomite  a  little  farther  east.  These  can  not  be  observed  because  of 
the  covei-ing  of  sandstone.  Their  position  is  appi-oximatel}^  indicated  on 
the  map  by  dotting  the  borders  of  the  several  belts.  The  thickness  of  the 
Traders  beds  across  this  area  and  the  position  of  the  southern  boundary 
of  the  dolomite  are,  of  course,  unknown.  The  former  is  arbitrarily  rep- 
resented as  having  the  same  width  as  it  has  north  of  the  Klondike  fold. 

The  absence  of  known  noteworthy  ore  deposits  in  this  area  is  probably 
accounted  for  by  the  general  absence  of  folding  or  brecciation.  Where 
the  Curry  member  is  narrowest,  and  where,  presumabh^,  more  or  less 
brecciation  exists,  is  the  deposit  of  the  Central  Vulcan  shafts.  On  the 
Traders  belt  the  only  promising  exploration  is  Jones's  shaft,  and  it  is 
significant  that  this  is  near  the  fold  in  the  Traders  beds  corresponding  to 
the  Klondike  fold  in  the  Curry  beds. 
MON  XLVI — 04 29 


450 


THE  MENOMINEE  IRON-BEARING  DISTRICT. 


EAST   VULCAN    MINE. 


This  area  extends  through  the  southwestern  portion  of  sec.  11,  T.  39  N., 
R.  29  W.,  just  east  of  the  Central  Vulcan  area  (PI.  XXXV).  In  it  are 
the  Nos.  1,  3,  and  4  shafts  of  the  East  Vulcan  mine  and  east  of  it  the  one 
shaft  of  the  Verona  mine.  The  Vulcan  beds  occur  on  the  side  of  the 
same  ridge  that  extends  all  the  way  from  the  Cuny  mine,  and  which  is 
bordered  everywhere  by  the  iron-bearing  formation.  The  top  of  this  ridge 
is  covered  with  the  sandstone  that  presents  in  so  many  areas  an  uncon- 
querable obstacle  to  the  investigation  of  the  Huronian  rocks.  Fortunately, 
this  sandstone  covering  overlaps  the  iron-bearing  beds  to  only  a  slight 
extent,  its  southei'u  boundary   being  nearly   coincident  with  that   of  the 


Fig.  51. — Horizontal  section  of  East  Vulcan  mine  at  eighth  level,  No.  4  shaft. 

Randville  dolomite.  It  is  usually,  however,  a  little  south  of  the  southern 
limit  of  the  dolomite;  hence  the  exact  position  of  this  can  only  be  indicated 
approximately.  Just  west  of  the  west  line  of  sec.  11  the  Brier  slate  widens 
and  passes  into  the  section  as  a  belt  500  to  600  feet  in  width.  About  a  hun- 
dred yards  farther  east  this  belt  divides  into  two  belts,  separated  from  one 
another  by  a  belt  of  iron-bearing  beds,  which  is  interposed  between  the 
Traders  belt  to  the  north  and  the  belt  of  Curry  beds  to  the  south  Between 
this  place  and  the  meridian  of  shaft  No.  4  there  are  therefore  in  a  section 
across  the  Vulcan  formation  three  belts  of  iron-bearing  beds  and  two  of 
Bner  slate.     Farther  east  the  middle  and  southern  iron-bearing  belts  appear 


U,  S.  GEOLOGICAL  SURVEY 


MONOGRAPH     XLVI       PL. XXXV 


Base  of  this  map  furnished  by  Pennlron  Mining  Company 


ALGONKIAN,  THE  ORE  DEPOSITS. 


451 


to  coalesce  in  consequence  of  the  disappearance  of  the  southern  belt  of 
Brier  slate.  Beyond  to  the  east,  as  far  as  the  Sturgeon  River,  only  two 
iron-bearing  belts  and  one  slate  belt  are  known.  A  study  of  the  distribu- 
tion of  the  slates  as  exposed  by  ledges  and  test  pits  near  the  west  line  of  the 
section  shows  clearly  that  the  slates  wrap  around  the  western  end  of 
the  middle  ore-bearing  belt  and  that  at  the  turn  their  beds  are  broken  and 
contorted  into  many  little  folds  pitching  east.     The  southern  belt  of  Brier 


'  ' ''"  \^''^''"'''^!''^^^^^^ 


eOi  leuel    1^ 


Fig.  52. — Vertical  north-south  cross  section  through  shaft  No.  3,  East  Vulcan  mine.    The  general  dip  of  the  beds  is  to 

the  south. 

slates  becomes  thinner  to  the  east  and  on  the  eighth  level  of  shaft  No.  4  it 
is  only  10  or  15  feet  thick  (fig.  51).  Thus  the  middle  belt  of  the  iron- 
bearing  beds  is  a  syncline  of  the  Curry  member,  pitching  east,  and  the 
southern  belt  of  Brier  slates  a  closely  compressed  fold,  also  pitching  in 
the  same  direction.  The  cross  section  through  shaft  No  3  (fig.  52)  shows 
the  synclinal  character  of  the  intermediate  (northern  Curry)  jaspilite  belt 
very  beautifully.  If  we  assume  that  the  end  of  this  belt  is  only  a  short 
distance  below  the  sixth  level  of  the  mine,  the  pitch  of  the  fold  is  about  35°. 


452 


THE   MENOMINEE  IRON-BEARING  DISTRICT. 


On  the  plan  of  the  eighth  level  of  shaft  No.  4  (fig-.  53)  the  fold  in  the  Curry 
beds  again  appears. 

The  principal  ore  deposits  thus  far  exploited  in  shaft  No.  3  are  along 
the  sides  of  the  syncline  in  the  Curry  beds.     That  being  worked  from  shaft 

No.  4  is  in  the  Traders  beds,  parti}' 
on  the  contact  of  these  with  the 
overlying  Brier  slate  (see  fig.  53). 
The  dip  of  the  contacts  is  about 
60°  S.  The  onl}'  indication  of 
the  j)resence  of  the  dolomite  in 
this  area  is  the  existence  of  talcose 
slates  north  of  the  Traders  jaspi- 
lites  on  the  eighth  level,  shaft  No. 
4.  The  contact  between  the  two 
formations  projected  to  the  sur- 
face would  make  the  surface  con- 
tact occur  under  the  sandstone 
covering  about  300  feet  north  of 
shaft  No.  4.  On  the  map  (PI. 
XXXV)  the  Traders  belt  is  repre- 
sented as  of  uniform  width  across 
the  area,  making  the  southern 
boundary  of  the  dolomite  parallel 
with  the  southern  boundary  of  the 
Traders  beds.  Tliat  this  contact 
is  sinuous  can  hardly  be  doubted. 
It  is  probable  that  it  is  deeply 
indented. 

West  of  shaft  No.  3  the  expo- 
sures are  abundant.  The  strikes 
and  dips  observed  confirm  the 
inferences  outlined  above  with  re- 
spect to  the  existence  of  a  large  fold  in  the  Curry  beds  at  this  place.  The 
Brier  slate  is  very  much  contorted  beyond  the  observed  termination  of  the 
northern  belt  of  the  Curry  beds,  and  the  exposures  of  the  latter  indicate 
that  these,  too,  are  folded.     A  little  exposure  just  east  of  shaft  No.  3,  for 


Fig.  53. — Vertical  north-south  cross  section  through  shaft  No.  4, 
East  Vulcan  mine.    The  dip  of  the  beds  is  to  the  south. 


Q 

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ALGONKIAN,  THE  ORE  DEPOSITS.  453 

instance,  shows  a  strike  of  N.  15°  W.,  i.  e.,  nearly  transverse  to  the  direction 
of  the  belt,  and  a  dip  87°  E. 

East  of  shaft  No.  3  the  exposures  and  test  pits  are  comparatively  few. 
The  several  belts  appear  to  continue  with  approximately  uniform  width  to 
the  center  of  the  section  (north-south  quarter  line). 

VEKOXA    MINE. 

The  Verona  area  is  east  of  the  East  Vulcan  location.  It  occupies  the 
southern  half  of  the  southeast  quarter  of  sec.  1 1  and  the  northern  portion 
of  the  adjoining  sec.  14.  The  mine  shaft,  which  was  formerly  known  as 
Southeast  Vulcan,  is  situated  near  the  south  line  of  the  southwest  quarter 
of  the  southeast  quarter  of  sec.  1 1 . 

Information  concerning  the  geology  of  the  area  is  scanty,  since  rock 
exposures  are  few  and  the  ground  has  not  been  explored  to  any  great 
extent.  In  the  cuts  alongside  the  railroad  track  west  of  the  Verona  mine 
the. Curry  jaspilites  are  exposed  in  long  ledges  striking  N.  70°  to  80°  W. 
and  dipping  about  vertically  or  very  high  to  the  north.  In  the  Woods 
shaft,  southeast  of  the  Verona  shaft,  the  contact  of  the  Hanbur}^  slate  with 
the  Curr}^  beds  dips  75°  to  80°  S.  The  normal  dip  over  most  of  the  area 
seems  to  be  to  the  south  at  high  angles,  as  it  is  for  some  distance  to  the  west, 
but  here  and  there  for  short  distances  the  beds  are  overturned  to  the  north. 

The  Traders  member  has  been  traced  by  test  pits  and  an  exploring 
shaft  nearly  to  the  east  edge  of  the  section,  but  ver}-  little  has  been  learned 
of  its  structural  features. 

The  ore  deposit  in  the  Verona  mine  has  been  only  partially  explored. 
So  far  as  now  known,  it  comprises  an  ore  body  in  the  Currv  member. 
Drill  holes  put  in  to  the  south  of  the  .seventh  level,  near  its  east  end, 
penetrated  a  belt  of  Brier  slate  that  apparently  lies  between  two  belts  of 
jasper,  which  farther  west  unite  and  form  a  single  belt.  This  may  indicate 
the  presence  of  a  fold  in  the  iron-bearing  series,  but  its  exact  nature  has 
not  yet  been  ascertained. 


EMMETT    AND    BKEEN    MIXES. 


These  min^s  are  situated  at  the  village  of  Waucedah,  in  sec.  22,  T.  39 
N.,  R.  28  W.  (PL  XXXVl).  They  were  the  first  mines  opened  on  the 
Menominee  range,  and  consequently  have  been  more  fully  described  than 
any  others  in  the  district.     From  the  descriptions,  however,  verv  little  can 


454  THE  MENOMINEE  IRON-BE AKING  DISTRICT. 

be  gleaned  with  reference  to  the  occurrence  of  the  ores.  At  present  the 
difficulties  met  with  in  attempting  to  decipher  their  geolog)-  are  almost 
insurmountable.  The  great  open  pits  are  full  of  water.  Sandstone  covers 
the  ore-bearing  beds  in  many  places,  resting  upon  a  very  irregular  pre- 
Cambrian  surface,  and  therefore  in  some  instances  reaching  considerable 
distances  beneath  the  present  surface.  Moreover,  the  basal  layers  of  this 
sandstone  are  often  highly  ferruginous,  sometimes  consisting  mainly  of 
hematite  intermingled  with  a  small  portion  of  siliceous  and  other  impurities. 
These  ferruginous  beds  resemble  very  closely  some  of  the  Traders  slates 
elsewhere,  consequently  it  is  exceedingly  difficult  to  identif}^  them  as 
Cambrian.  Further,  the  ore-bearing  beds  exposed  in  the  mining  pits  and 
in  their  innnediate  ^^icinity  contain  much  more  fragmental  material  than  has 
been  encountered  elsewhere.  The  thin  sections  show  great  numbers  of 
round  and  sharp-edged  quartz  grains,  much  muscovite  and  other  light- 
colored  micaceous  minerals,  light-green  earthy  substances  resembling 
serpentine,  and  occasional  clastic  grains  of  feldspars.  The  ore  is  in  little 
bands  between  these  components  and  in  well-defined  naiTow  layers 
interl)edded  with  layers  composed  principally  of  the  siliceous  minerals. 

To  the  west  of  the  mine  pits  much  more  typical  cherts  and  jaspilites 
are  found,  not  only  in  the  dumps  of  the  numerous  test  j)its  scattered  over 
the  area,  but  also  in  natural  ledges.  By  the  aid  of  these  pits  the  three 
separate  belts  of  the  Vulcan  formation  can  be  traced  entirely  across  sec.  22, 
and  their  limits  with  reference  to  one  another  can  be  delimited  with  a  fair 
degree  of  accuracy.  On  the  other  hand,  the  exact  boundary  of  the 
formation  with  respect  to  the  dolomite  on  the  north  and  the  Hanbury  slate 
on  the  south  can  be  indicated  only  approximately,  the  former  because  of 
the  sandstone  covering  and  the  latter  because  of  lack  of  exposures  of  the 
slates. 

The  Traders  belt  enters  the  section  from  the  west  at  the  northwest 
corner,  continues  east  to  the  north-south  quarter  line,  and  then  trends 
east  of  north  and  leaves  the  area  between  the  north  quarter  post  and  the 
nortlieast  corner  of  the  section,  its  southern  boundary  passing  through 
the  corner  or  a  few  feet  north  of  it.  The  belt  is  traced  almost  exclusively 
by  test  pits  and  shafts,  but  near  the  quarter  post  there  is  a  large  craggy 
ledge  of  cherts  and  jaspilites  that  suggests  more  strongly  the  Curry  beds 
than  the  Traders.     At  the  southwest  corner  of  the  ledge  there  is  an  excellent 


U    S    GEOLOGICAL    SURVEY 


MONOGRAPH     XLVI     PL.XXXVII 


LEGEND 

CAMBRIAN 


LakeSyperioraandsione 

I  undxHymg  ftmnalutna 
shown  where  known  > 


oiily  sandstone 

ALGONKIAN 

[   Ah  J 
Haubun,-  nlate 


Randville  dolomite 


Expoaures.dip  and 

strike  noi  shown 

f  a  U  Lake  ^uptnorsaiuistont 

erposunsarvhoritonlal  I 


Exposures  with  observed 
dipand strike 


Tunnels 
^9° 


Magnetic  declinalion 


Magnetic  dip 


Mining  pits 


GEOLOGIC  MAP  OF  PORTIONS  OF  SECS.  25.  26.  35,AND.36.T.  40  N.,R.31  W..MICHIGAN 

BY  W  S  BAVLEY 
1903 
Scale 
1000  500  o 1000  zooofeet 


ALGONKIAN,  THE  ORE  DEPOSITS.  455 

exhibition  of  the  "bands  and  shots"  of  ore  in  a  white  or  gray  pellucid  chert. 
The  shots  are  spherical  masses  of  hematite  about  the  size  of  a  small 
buckshot,  and  the  bands  are  chains  of  these  lying-  side  by  side  in  a  line. 

The  Brier  slate  is  shown  in  a  number  of  pits  and  in  sevei-al  small  ledges. 
The  rocks  exposed  have  the  typical  aspect  of  these  slates  in  the  greater 
number  of  instances,  but  in  others  they  are  strongly  ferruginous  and  cherty. 
This  is  particularly  so  near  the  west  side  of  the  northeast  quarter  of  the 
northwest  quarter  of  the  section  where  the  rocks  are  contorted  into 
numerous  small  folds.  These  folds,  which  pitch  west  at  angles  of  about 
30°,  indicate  the  presence  of  a  larger  fold  in  the  neighborhood  which  may 
have  caused  an  accumulation  of  ore  in  the  folded  rocks.  The  position  of 
this  larger  fold  can  not  be  mapped  with  oiu-  present  knowledge  because 
of  the  lack  of  sufficient  exposures. 

The  Curry  belt  is  not  as  well  delimited  in  the  western  portion  of  the 
section  as  are  the  other  two  belts  of  the  Vulcan  formation.  A  few  pits  south 
of  the  Brier  slates,  however,  are  bottomed  in  an  iron-bearing  formation 
which  must,  from  its  position,  be  the  Gurry  member.  Near  the  north-south 
quarter  line,  however,  and  east  to  the  east  line  of  the  section,  test  jjits  that 
have  uncovered  the  Curry  member  are  frequent,  and  the  large  open  pits  of 
the  Emmett  and  Breen  mines  leave  no  doubt  as  to  the  existence  of  an  iron- 
bearing  series  between  the  Brier  and  the  Hanbury  slates.  This  series  of 
rocks  dips  south  at  about  70°.  Natural  exposures  are  to  be  seen  at  the 
westernmost  of  the  Emmett  pits.  The  jaspilites  and  the  ores  associated 
with  them  are  exceedingly  sandy  looking,  and,  as  has  been  mentioned,  they 
contain  an  abundance  of  clastic  quartz  grains.  Nowhere  in  this  area  are 
the  distinctly-banded  jaspilites  met  with,  except  perhaps  in  a  few  of  the  pits 
in  its  western  portion. 

Summary. 

The  above  brief  description  of  the  mines  will  serve  to  show  that  the 
ore  deposits,  where  of  any  magnitude,  are  situated  in  just  such  positions 
with  respect  to  the  surrounding  rocks  as  might  have  been  predicted  on  the 
assumption  that  the  accumulation  of  the  ores  is  the  result  of  the  action  of 
percolating  ground  waters.  The  larger  and  richer  deposits  are  without 
exception  in  the  troughs  of  pitching  synclines.  The  smaller  and  leaner 
deposits  are  along  such  contacts  as  would  naturally  be  followed  by  descend- 
ing currents.     Where  the  rocks  are  brecciated  near  the  contacts  the  removal 


456  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

of  silica  has  proceeded  with  greater  completeness  than  along  contacts  where 
there  has  been  no  brecciation  and  the  ores  are  consequently  rich.  Where 
brecciation  is  lacking  the  ores  are  leanest.  Where  folding,  brecciation,  and 
other  marked  disturbances  are  lacking  there  the  ores  are  lacking  also. 

OTHER    LOCALITIES    OF   THE   VULCAN    FORMATION. 

There  are  several  other  areas  along  the  southern  ore-bearing  belt 
where  the  Vulcan  formation  is  present,  but  from  which,  so  far  as  is  now 
known,  merchantable  ore  deposits  are  absent.  These  emphasize  the  state- 
ments made  above  as  to  the  manner  of  occurrence  of  the  ore  bodies,  since 
they  serve  to  show  that,  in  the  absence  of  marked  disturbances  in  the 
jaspilite  belt,  there  is  not  much  hope  for  the  discovery  of  valuable  deposits. 

Sees.  25  and  26,  T.  40  N.,  B.  31  W. — The  westernmost  point  at  which 
any  member  of  tlie  southern  belt  of  the  Vulcan  formation  has  been  observed 
is  at  about  the  center  of  the  northwest  quarter  of  sec.  26,  T.  40  N.,  R.  31  W. 
(PI.  XXXVIl).  From  this  point  a  series  of  pits  and  shafts  extends,  with 
short  intervals  between  them,  all  the  way  to  the  east  side  of  sec.  25,  but 
they  cover  only  a  naiToyv'  strip  of  territory  running  through  the  district,  and 
so  sfive  very  little  evidence  as  to  the  conditions  undero-round.  That  the 
Vulcan  formation  exists  from  one  end  of  the  district  to  the  other  admits  of 
,no  doubt.  A  jaspilite  belt  stretches  throughout  the  entire  distance,  and  this 
is  bordered  on  the  south  by  a  series  of  slates.  In  some  places  the  slates  are 
red  and  earth}'.  In  other  places  they  are  mottled  sericitic  varieties,  and  in 
still  other  places  they  resemble  some  phases  of  the  Brier  slates.  Some  of 
these  slates  are  unquestionably  Hanbury.  Whether  others  are  Brier  or  not 
it  is  impossible  to  say  at  present.  The  northern  margin  of  the  jaspilite  belt 
appears  to  have  been  reached  by  the  most  northerly  of  the  drill  holes  through 
the  sandstone  in  the  vicinity  of  the  Federal  exploration  in  the  western  portion 
of  sec.  25  and  in  drifts  running  north  from  the  more  northerly  shaft  in  sec. 
26.  In  both  these  places  the  rock  bordering  the  jaspilite  is  either  tlie 
Randville  dolomite  or  the  cherty  quartz  rock  lying  above  this.  At  the  old 
Ludington  mine,  near  the  center  of  the  southeast  quarter  of  sec.  25,  the 
dump  contains  in  abundance  large  fragments  of  coarse  quartzite  like  that 
at  the  base  of  the  Traders  member  and  pieces  of  jaspilite  that  are  identical 
in  appearance  with  the  Traders  jaspilites  at  the  Aragon  mine.  Moreover, 
the    situation    of  the  old    Ludington  works   with  respect   to  the  jDresent 


Wic 

is      e- 

S-    nc-l'^   1 1 

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Jiic 

&     \ 

"^t- 

^ 

SH 

ALGONKIAN,  THE  ORE  DEPOSITS.  457 

Ludingtoii  mine  indicates  that  both  mines  are  at  the  same  geological 
horizon,  i.  e.,  the  horizon  of  the  Traders  member.  Passing  westward,  the 
conditions  seem  to  be  the  same  at  the  explorations  in  the  center  of  sec.  25. 
Farther  west  the  jaspilite  belt  is  narrow  and  is  bordered  on  the  south  by 
slates  closely  resembling  the  Brier  slates.  It  is  probable,  indeed  almost 
certain,  that  near  the  west  line  of  sec.  25  only  one  jaspilite  belt  is  present, 
and  this  along  its  upper  contact  at  the  Federal  exploration  contains  an  ore 
body  110  to  115  feet  in  width.  The  contact  dips  south  at  85°.  At  several 
other  points  lean  ores  have  been  found,  but  nowhere  else  has  a  distinct  and 
well-defined  ore  body  been  discovei-ed. 

Just  east  of  the  east  line  of  the  area  now  being  discussed  all  three 
members  of  the  Vulcan  formation  are  known  in  complicated  folds  that  have 
caused  a  repetition  of  the  members  in  several  belts  These  have  been 
traced  westward  to  within  a  few  hundred  feet  of  the  east  line  of  sec.  25,  but 
have  there  been  lost  because  of  lack  of  exposures  and  of  explorations.  Until 
these  sliall  have  l)een  followed  continuously  into  sec.  25  the  manner  and 
place  of  their  disappearance  can  not  even  be  conjectured  and  the  problem 
of  the  geology  of  this  section  and  the  one  to  the  west  must  be  left  unsolved. 
The  overla})ping  of  the  sandstone  beyond  the  southern  limit  of  the  Randville 
dolomite  prevents  the  detection  of  folds  in  this  formation,  if  they  exist,  and 
the  character  of  the  explorations  in  the  jaspilite  belt  has  not  been  such  as 
to  develop  the  folds  that  may  be  present  in  it.  It  may  be  that  folds  of 
large  size  exist  in  the  center  of  sec.  25,  since  both  sharp  and  smooth  folding 
on  a  large  scale  is  noted  in  many  of  the  jaspilite  fragments  on  the  dump  of 
the  deep  shaft  at  this  place;  but,  if  so,  there  is  no  evidence  on  the  surface 
to  indicate  the  fact. 

Sec.  33,  T.  40  N.,  B.  30  TF.— This  section  lies  between  the  Keel  Ridge 
location  (PI.  XXIX)  and  the  Quinnesec  and  Cundy  mines  (PI.  X.\X).  The 
explorations  along  the  iron-bearing  belt  across  the  section  are  not  suffi- 
ciently numerous  to  give  much  idea  as  to  the  distribution  of  the  underlying 
rocks.  An  iron-bearing  belt  enters  the  southwestern  corner  of  the  section, 
and  leaves  the  southeastern  corner  (PI.  XXXVIII).  From  the  scanty 
information  at  hand  it  appears  to  lie  between  the  Hanbury  slate  to  the 
south  and  a  quartzite  or  slate  to  the  north.  The  former  is  believed  to  be 
the  cherty  phase  of  the  Randville  dolomite  that  lies  above  the  more  purely 
dolomitic  beds,  and  the  latter  is  thought  to  be  a  phase  of  the  Brier  sla,te. 


458  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

This  belt  apparently  disappears  by  overlap  in  the  center  of  the  sontheast 
quarter  of  the  section  and  gradually  thickens  both  to  the  east  and  the 
west.  At  this  place,  too,  there  is  some  evidence  of  the  northward  bending 
of  the  iron-bearing  belt,  which  may  indicate  a  corresponding  northward 
embavment  in  the  dolomitic  margin  and  a  gentle  fold  in  the  entire  Vulcan 
formation.  No  ore  deposits  have  thus  far  been  developed  within  the  area. 
This  is  not  surprising  if  the  iron-bearing  member  is  the  Curry  member, 
especially  if,  as  appears  to  be  the  case,  there  is  no  sharp  folding  to  cause 
brecciation  in  the  jaspilites  or  to  furnish  troughs  for  the  accumulation  of 
the  ores. 

North  of  the  Vulcan  beds  the  dolomite  is  exposed  in  a  number  of 
large  exposures  in  the  western  portion  of  the  section.  It  has  likewise  been 
found  in  drill  holes  and  a  shaft  in  its  extreme  eastern  portion.  Elsewhere 
north  of  the  northern  boundary  of  the  Vulcan  beds  only  sandstone  is 
known.  At  two  places  this  has  furnished  some  ore  from  the  conglomerates 
at  its  base. 

Sees.  1  and  2,  T.  3,9  N.,  B.  30  W. — This  area  is  east  of  Quinnesec  and 
between  this  village  and  sec.  6,  T.  39  N.,  R.  29  W.,  to  be  referred  to  later. 
There  are  no  natural  exposures  of  the  Vulcan  formation  or  of  the  Hanbury 
slate  in  the  area,  although  exposures  of  the  Randville  dolomite  are 
abundant,  especially  in  sec.  2,  T.  39  N.,  R.  30  W.,  and  in  sec.  35  lying  to 
the  north  (PI.  XXXIX).  A  large  number  of  explorations  have,  however, 
been  made  in  the  area  and  these  have  afforded  a  large  number  of  facts 
from  which  the  geological  structure  may  be  inferred.  The  dolomite 
exposures  in  sees.  2  and  35  have  been  described  in  another  place  (see  p.  263 
et  seq.).  The  soutliern  boundary  of  the  formation  in  sec.  1  is  determined 
with  a  fair  degree  of  accuracy  by  exposures,  pits,  and  drill  holes.  Its 
northern  boundary  can  be  established  only  approximately,  as  the  usual 
layer  of  sandstone  covers  all  the  northern  portion  of  the  area  underlain  by 
this  dolomite.  Drill  holes  in  the  southwest  quarter  of  the  southeast  quarter 
of  sec.  35,  and  a  test  pit  near  the  north  line  of  sec.  1  indicate  that  the 
boundary  is  north  of  these  points.  Along  the  line  between  sees.  1  and  2 
the  dolomite  belt  is  shown  by  drill  holes  and  test  pits  to  be  continuous  from 
the  corner  to  the  Bryngelson  shaft,  about  1,600  feet  south  of  the  corner. 
Its  southern  boundary  is  a  continuous  straight  line  without  indentations 
of  any  kind  which  would  indicate  the  presence  of  folds. 


U    S    GEOLOGICAL    SURVEY 


MONOGRAPH   XLVI      PL    XXXIX 


us  RIEN&CO  IITM   ^ 


c;i<:OLOtVI('  map  OPrOUTIOTs'S  OFSECS.IAXD  2,T.  :59N..R.30W 
AN  D  S  EC  S .  35  AN  D  36.  T.  40  N ..  H .  3  O  W,  M I T 1 1 1 GAN 

BY  W  S  B.VliXKY 


LEGEND 
CAMBRIAN 


[.akeSupenorsandstoiie 
I  tmdtrlyini}  ronnationa 
sfii/tviiw/ierv Kiiuwn  j 


Test  pits,  exposing 
only  sandstone 


ALGONKIAN 
Ah 


llanbnry  slate 


Ab 

Uner  slate 

Inidi-'rs  member 


Ar 

Haiidvilloiloloiimc 


Exposures, dip  and 
strike  uoi  shown 

lain  oAr  Sup  rrwrsaitdjtun  r 
erposiirtJiafYhoritoniiil  • 


Exposures  with  strike 
Dip  not  observod 


Exposureswithobserved 
dipandstriki? 


Teal  pils 


Magnetic  dip 
FoldHwtlliobaervpd  pltuli 


ALGONKIAN,  THE  ORE  DEPOSITS.  459 

South  of  the  dolomite  the  Vulcan  beds  should  normally  occur.  To 
the  west  of  sec.  2  the  three  members  of  the  formation  have  been  observed, 
but  there  are  no  exposures  or  explorations  in  the  western  half  of  the 
section  by  which  they  can  be  traced  across  the  line.  The  magnetic  line 
which  is  so  strong  in  the  neighborhood  of  the  Cundy  mine  enters  the 
section  from  the  west  but  gradually  dies  out  within  a  quarter  of  a  mile  of 
its  west  line.  Near  the  center  of  sec.  1,  in  the  eastern  portion  of  the  area, 
a  drill  hole  penetrated  a  few  feet  of  lean  ore  lying  between  Hanbury  slates 
and  a  narrow  band  of  gray  slates  between  it  and  the  dolomite.  The  entire 
Vulcan  series  at  this  place  is  not  30  feet  thick. 

Between  this  drill  hole  and  the  western  line  of  sec.  2  the  explorations 
have  shown  only  Hanbury  slate  south  of  the  dolomite.  This  is  often 
graphitic  near  the  dolomite  and  is  in  some  places  traversed  by  a  great 
many  quartz  veins.  In  the  Bryngelson  shaft  and  in  a  trench  a  few  feet  to 
the  west  the  slate  is  in  contact  with  the  dolomite  (see  p.  366),  so  that  there 
is  no  possibility  of  the  presence  of  the  Vulcan  beds  between  them.  The 
complete  disappearance  of  the  Vulcan  formation  after  entering  the  area 
from  the  west  and  its  gradual  thinning  as  it  enters  the  area  from  the  east 
is  explained  as  due  to  overlap  of  the  Hanbury  slate  along  a  sinking  shore 
line  (see  pp.  370-372). 

Sec.  6,  T.  39  N.,  B.  29  W. — This  section  has  probably  proved  more 
disappointing  to  explorers  than  any  otlier  in  the  entire  Menominee  district. 
In  the  search  for  the  westward  extension  of  the  Norway  and  Aragon  ore 
deposits  an  immense  amount  of  money  has  been  expended  in  explorations, 
and  even  now,  with  the  results  of  all  these  explorations  in  hand,  we  are 
nevertheless  still  very  much  in  the  dark  as  to  the  geology  of  the  section. 
There  seems,  however,  to  be  no  possibility  of  the  existence  of  undiscovered 
folds  in  the  area,  and  therefore  not  much  possibility  of  the  presence  of 
large  ore  deposits  comparable  with  those  of  the  Norway  and  Aragon 
mines. 

The  succession,  beginning  at  the  north,  is:  Dolomite,  followed  by 
light-colored  slates  that  are  talcose  in  part,  and  in  part  quartzose;  coarse 
quartzite,  like  that  elsewhere  near  the  base  of  the  Traders  beds;  a  jaspilite 
belt  from  250  to  450  feet  in  width,  and,  finally,  a  wide  belt  of  slate  (PI.  XL). 
The  boundary  between  the  Lower  and  the  Upper  Menominee  is  drawn  at 
the  top  of  the  talcose  slates.     The  Vulcan  beds  dip  south  at  angles  varying 


460  THE  MENOMINEE  IKON-BEARING  DISTRICT. 

between  55°  and  70°,  and  strike  nearly  east-west.  The  southern  slate  at 
some  places  is  in  some  respects  like  the  typical  Brier  slate;  at  other  places 
it  is  the  typical  gray  slate  of  the  Haubmy  formation.  Its  maximum  width, 
as  developed  by  drilling,  is  about  400  feet.  South  of  this  point  the  nature 
of  the  underlying  rock  is  unknown.  It  is  possible,  of  course,  that  the  slate 
is  Brier  and  that  elsewhere  to  the  south  is  a  second  jaspilite  belt,  and  that 
the  Hanbury  slate  is  much  farther  south.  On  the  map  the  slate  in  which 
the  drills  were  put  down  is  placed  in  the  Hanbury  formation.  This  would 
make  the  jaspilite  belt  to  the  north  represent  the  Curry  member,  unless  this 
member,  together  with  all  the  Brier  slate,  is  absent,  and  this  is  not 
considered  probable.  The  true  age  of  the  iron-bearing  beds  and  the  slate 
to  the  south  of  them  can  not  be  determined  until  the  hiatus  between  the 
Norway  and  Cyclops  mines  and  the  west  line  of  sec.  5  has  been  explored 
sufficiently  to  enable  one  to  trace  the  tlu-ee  members  of  the  Vulcan 
formation  from  the  mines  westward  into  sec.  6. 

Where  it  enters  the  section  from  the  east  the  jaspilite  belt  is  about  250 
feet  wide.  It  keeps  this  breadth  uniformly  to  near  the  center  of  the  section, 
where  it  gradually  widens  to  about  400  feet  or  450  feet,  and  beyond  the 
center  it  again  contracts  slightly.  The  expansion  near  the  center  of  the 
section  is  e^■idently  due  partly  to  folding. 

In  the  open  pit  east  of  the  shaft  north  of  the  old  electric-light  works 
the  jaspilites  are  well  exposed  in  sharp  folds  pitching  west.  Tlie  dip  in 
places  is  70°  N.  Since  the  dip  farther  north  is  60°  S.,  there  may  be  a  fold 
in  the  beds  between  these  points.  Nowhere  else  in  the  belt  is  there  any 
evidence  of  the  presence  of  folds,  although  subordinate  folding  within  the 
formation  no  doubt  exists.  The  normal  dip  of  the  jaspilites  is  about  55°  to 
(jO°  S.  To  the  north  near  the  dolomite  it  becomes  flatter,  and  on  the  top 
of  the  hill  under  the  sandstone  it  is  quite  flat. 

The  rocks  are  typical  jaspilites  composed  of  alternating  layers  of 
schistose  hematite  and  dense  waxy  jasper.  The  jasper  is  often  in  flat 
lenticular  bands,  and  in  some  cases  these  bands  are  cherty  rather  than 
jasper  like. 

The  slate  belt  between  the  jaspilites  and  the  dolomite  appears  to  be 
much  wider  than  it  usuall}^  is,  but  this  great  width  may  be  due  to  the  flat 
dip  of  the  upper  surface  of  the  dolomite,  corresponding  to  the-  flat  dip  of  the 
overlying  jaspilites. 


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alCtOnkian.  the  ore  deposits.  461 

An  interesting  feature  of  some  of  tlie  deeper  pits  near  the  center  of  the 
section  is  the  presence  of  an  abundance  of  chert  on  their  dumps.  This  is 
usually  dark  colored,  flinty  and  very  much  brecciated,  the  fragments  con- 
sisting very  largely  of  a  pellucid  white  chert.  Large  bowlders  of  the  same 
chert  are  sometimes  found  inclosed  in  the  basal  layers  of  the  overlying 
sandstone.  Some  of  these  bowlders  are  finely  brecciated,  but  others  consist 
of  the  dark  chert  traversed  by  veins  of  the  white  variety.  The  fragments 
in  the  brecciated  phases  are  probably  shattered  portions  of  veins  of 
this  kind,  and  the  rock  is  probably  fi'om  a  chert  layer  at  the  top  of  the 
dolomite. 

Sees.  12  and  13,  T.  39  N.,  R.  29  W. — The  most  easterly  exposures  of 
the  Vulcan  formation,  with  the  exception  of  those  occurring  at  Waucedah, 
are  to  be  found  on  the  west  side  of  the  Sturgeon  River,  near  the  north 
quarter  post  of  sec.  13,  T.  39  N.,  R.  29  W.  (PL  XLI.)  The  greater 
portion  of  the  south  half  of  the  section  to  the  north  is  occupied  by  the 
Randville  dolomite,  the  exposures  of  which  have  been  described  on  pre- 
ceding pages  (pp.  271-273).  N,orth  of  the  dolomite  the  country  is  supposed 
to  be  underlain  by  a  westward -pitching  syncline  of  the  Hanbury  slate, 
and  northeast  by  an  eastward-pitching  syncline  of  the  Vulcan  formation 
(see  pp.  404-407).  On  the  south  the  dolomite  is  bordered  by  a  belt  of 
the  Vulcan  formation  about  900  feet  wide,  and  south  of  this  is  the  Han- 
bury slate. 

The  Vulcan  beds  are  exposed  by  trenches  and  test  pits,  near  the  north- 
south  quarter  line  of  sec.  13  and  by  a  group  of  pits  near  the  center  of  the 
northwest  quarter  of  the  northwest  quarter  of  the  section.  All  three 
members  of  the  formation  are  represented  in  their  typical  development. 
The  jaspilites  in  the  trench  strike  east-west  and  dip  vertically.  The  dump 
of  the  northernmost  pit  near  the  southernmost  ledges  of  dolomite  shows  the 
usual  coarse  quartzite  at  the  base  of  the  Traders  member,  and  the  talcose 
slates  that  usually  separate  the  Traders  quartzites  and  jaspilites  from  the 
dolomite.  This  latter  rock  nearest  the  contact  with  the  overlying  Vulcan 
beds  is  brecciated,  and  some  specimens  of  the  breccias  look  very  conglom- 
eratic Close  search  through  the  conglomeratic  phases,  however,  revealed 
no  foreign  fragments  that  might  indicate  that  the  rock  was  water  deposited. 


462  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

HANBURY  SLATE. 
DISTRIBUTION  AND  TOPOGRAPHY. 

The  Hanbuiy  slate  occurs  mainly  iu  three  large  belts  constituting 
valleys  that  correspond  with  synclines  between  the  older  rocks.  It  occu- 
pies nearly  all  the  low  ground  in  the  Menominee  trough,  forming  a  plain 
broken  only  by  heaps  of  glacial  material  deposited  upon  it,  by  the  protru- 
sions of  a  few  hillocks  composed  of  the  harder  slates,  or  by  equally  resistant 
greenstones.  Exposures  in  the  slate  areas  are  very  rare  and  widely  scat- 
tered. They  are  confined  almost  exclusively  to  the  hillocks  to  which 
reference  has  been  made  and  to  the  lower  slopes  of  some  of  the  stream 
valleys.  The  slates  are  also  exposed  in  a  number  of  places  on  the  sides  of 
cuts  along  the  railroad  right  of  way. 

Since  the  main  part  of  the  Menominee  trough  is  a  westward-pitching 
synclinorium  the  slate  areas  are  narrowest  at  the  east  and  gradually  widen 
toward  the  west.  The  northern  belt  is  divided  into  two  portions  by  the 
western  area  of  Quinnesec  schists.  The  northern  part  turns  northwest  and 
leaves  the  Menominee  district  at  the  northern  limit  of  the  area  mapped, 
while  the  southern  portion  coalesces  with  the  middle  belt  and  crosses  the 
Menominee  River  into  Wisconsin.  East  of  Iron  Hill  the  two  northern  belts 
again  coalesce  and  extend  as  a  single  belt  to  the  Sturgeon  River.  Near  the 
longitude  of  Waucedah  all  the  slates  disappear  to  the  east  beneath  the 
Paleozoic  beds. 

LITEOLOGY. 

The  formation  comprises  black  and  gray  clay  slates,  gray  calcareous 
slates,  graphite  slates,  gray  wackes,  thin  beds  of  quartzite,  occasional  beds  of 
ferruginous  dolomite,  and  i-arer  bodies  of  ferruginous  chert  and  iron  oxide. 
These  rocks  present  no  unusual  characteristics.  The  argillaceous  slates  are 
like  normal  slates  elsewhere.  The  quartzites  and  graywackes  are  likewise 
normal.  The  calcareous  slates  are  either  fine-grained  quartzites  cemented 
by  a  calcareous  or  dolomitic  matrix,  or  are  normal  clay  slates  with  nests 
and  crystals  of  some  carbonate  scattered  through  their  masses.  The 
dolomites  and  cherts  are  like  those  in  the  Randville  and  Vulcan  formations. 

The  predominant  rocks  of  the  formation  are  the  gray  clay  slates  and 
the  calcareous  slates.  The  latter  are  more  abundant  in  the  lower  portions 
of  the  formation  and  the  former  in  the  upper  portions,  but  the  exact  vertical 


U.  S    GEOLOGICAL   SURVEY 


MONOGRAPH   XLVI      PL    XLI 


LEGEND 
ALGONKIAN 


Ah 


Hanbury  slate 


Ac 


Curry  member 

( irun-beanntf  t 


Ab 


US  eiE,N  S.  CO   LITH 


gp:ologic  map  qy 
PORTION  OF  SECS.  12  AND  13, T.  39  N.,R. 29  W.MICHIGAN 


BY  W.  S  BAYLEY 

1903 

Scale 


Traders  member 

<  iron-bea.rinq  I 


Randville  dolomite 


Exposures, dip  and 

strike  not  shown 

(ail  Lake  Superior  sandstone 

exposures  are  horizontal ) 


Exposures  with  observed 
dipand  strike 


Shafts 


Test  pits 


Trenches 


Magnetic  declination 


ZJ 


Magnetic  dip 


Line  of  maximum 
magnetic  dip 


o 


1000 


20oofeet 


ALGONKIAN,  HANBURY  SLATE.  463 

relations  of  the  two  rocks  have  not  been  made  out,  because  of  the  scarcity 
of  exposures  and  the  very  intricate  folding  to  which  they  have  been  subjected. 

The  formation  is  cut  by  dikes  of  schistose  greenstones,  and  in  one 
or  two  places  sheets  of  the  same  rock  have  been  intruded  between  the 
sedimentary  beds. 

Clay  slates. — The  clay  slates  are  mostly  gray  or  black  normal  argilla- 
ceous slates,  in  which  there  is  always  more  or  less  ferruginous  matter. 
Where  exposed  to  the  weather  they  are  light  in  color  and  have  a  shaly 
character.  Muscovite  or  sericite  then  becomes  prominent  and  tlieir  iron 
components  are  decomposed  to  red  ocherous  compounds.  Whei'e  most 
altered  the  rocks  are  light-red  sericite-slates  or  shales.  When  the  slates 
contain  small  quantities  of  calcareous  components  their  weathering  is  some- 
what different.  They  tend  to  bleach  to  a  very  pale-green  or  white  color 
and  to  become  porous  through  the  loss  of  their  calcareous  cement.  The 
ferruginous  components  oxidize,  forming  red  ocher,  and  this  lies  in  an 
irregular  pattern  on  the  light-colored  background.  The  result  of  these 
changes  is  a  red  and  white  or  pale-green,  mottled,  friable  slate,  known 
locally  as  "calico  slate."  A  few  varieties  of  the  black  slates  are  quartzose. 
These  are  denser  and  more  compact  than  the  more  purely  argillaceous 
varieties.  They  are  not  at  all  shaly  and  they  possess  little  or  no  slaty 
cleavage.     Tliese  rocks  grade  into  the  quartzites  and  graywackes. 

Under  the  microscope  the  argillaceous  varieties  of  the  clay  slates  are 
seen  to  consist  of  small  splinters  and  grains  of  quartz  and  an  occasional 
grain  of  feldspar  lying  in  a  crystalline  matrix  composed  of  interlocking 
quartz,  small  spicules  of  sericite,  kaolin,  and  chlorite,  larger  plates  of  the 
last-named  mineral,  and  the  usual  accessories  of  slates,  rutile  crystals  and 
needles,  limonite  clumps,  and  a  few  nests  of  calcite.  In  some  specimens 
the  sericite  preponderates  over  all  the  other  constituents;  in  others  the 
chloritic  component  is  in  excess,  and  in  yet  other  phases  quartz  is  most 
prominent.  Thus  the  normal  slates  pass  on  the  one  side  into  sericite-slates 
and  on  the  other  side  into  quartzite.  Usually  there  is  an  interlamination 
of  quaVtzose  and  chloritic  or  sericitic  beds  with  an  average  thickness  of  not 
more  than  one-fourth  inch. 

The  most  typical  sericite-slates,  or  perhaps  more  properly  schists,  differ 
from  the  argillaceous  ones  principally  in  the  greater  size  of  the  individual 
sericite    fibers.     Because    of    the    larger    dimensions    of    this    micaceous 


464  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

component  the  schistosity  of  these  slates  is  much  more  pi'onounced  than 
that  of  the  gray  and  black  argillaceous  phases. 

Upon  exposure  to  weathering  influences  many  of  the  argillaceous  and 
sericitic  slates,  as  has  been  stated,  pass  into  mottled  "calico"  slates.  The 
rocks  are  bleached  in  certain  places  by  the  alteration  of  the  greenish  sericite 
and  chlorite  into  colorless  compounds  except  near  cracks,  where  the  chlorite 
is  weathered  into  a  mass  of  ocher  and  quartz.  The  latter  change  causes 
red  staiiis  to  spread  out  from  the  walls  of  all  cavities  into  which  water  can 
penetrate,  thus  producing  red  irregularly  shaped  mottlings  against  the 
bleached,  white  background. 

The  graphitic  varieties  of  the  clay  slates  are  black,  very  fissile,  thinly 
laminated  rocks.  They  appear  to  be  limited  to  those  portions  of  the 
formation  near  its  contact  with  ferruginous  beds.  At  any  rate,  they  have 
been  seen  only  in  association  with  the  underlying  Curry  member  and  at 
horizons  a  few  hundred  feet  above  the  base  of  the  slate  formation,  where 
cherts  and  ores  have  been  developed,  but  they  do  not  everywhei'e  occur  at 
the  base  of  the  formation.  This  frequent  association  of  ore  and  grajihitic 
slates  suggests  the  possibility  of  a  genetic  relationship  between  them  which 
has  been  referred  to  in  another  place  (see  p.  354).  The  graphitic  slates 
appear  to  grade  laterally  into  the  normal  gray  slates,  of  which  they  seem 
to  be  local  moditications.  Since  they  occur  mainly  near  contacts  the 
graphitic  slates  have  usually  been  tremendously  sheared  into  very  thin  folia 
with  many  repeated,  complicated,  and  irregular  contortions.  When  stained 
by  ocherous  deposits  these  slates  are  recognizable  by  the  curved  or  convex 
character  of  the  plates  into  which  they  usually  split. 

Examined  microscopically  the  graphitic  slates  are  usually  very  fine 
grained.  They  contain  an  abundance  of  sericite  and  kaolin,  forming  an 
extremely  fine-grained  web  in  which  small  quartz  grains  are  embedded. 
The  graphite  coats  the  walls  of  shearing  joints.  It  is  observable  under  the 
microscope  only  when  the  sections  are  ])erpendicular  to  the  cleavage.  All 
specimens  are  schistose  in  parallel  positions,  and  the  calcite,  limonite,  and 
most  of  the  crystallized  quartz  grains  are  elongated  in  the  same  direction. 
In  many  sections  microscopical  folds  are  visible  which  are  counterparts  of 
the  folds  seen  in  hand  specimens. 

Grayivaches  and  quartzites. — The  graywackes  and  quartzites  of  the 
Hanbury  formation   are  normal  rocks  of  their  kind,  requiring  no  special 


ALGONKIAN,  HANBURY  SLATE.  465 

description.  They  both  occur  in  comparatively  thin  beds  interlaminated 
with  slates,  more  frequentl}^  in  the  lower  part  of  the  formation  than  in  tlie 
upper  portion.  The  quartzites  are  more  abundant  than  the  graywackes, 
but  neither  are  common. 

In  one  place  only  within  the  district  is  the  quartzite  present  in  any 
considerable  quantity.  This  is  near  the  ])oint  where  the  Chicago  and 
Northwestern  Railway  crosses  the  line  between  sec.  19  in  T.  40  N.,  R.  30 
W.,  and  sec.  24,  T.  40  N.,  R.  31  W.  In  the  cut  through,  which  the  right  of 
way  runs  beautifully  banded  slates  are  exposed,  striking  in  general  N. 
75°  W.  and  dipping  nearly  vertically.  With  these  are  interbedded  narrow 
bands  of  quartzite  or  graywacke.  The  slates  are  distinctly  ripple  marked, 
and,  together  with  the  quartzites,  are  compressed  into  little  folds  pitching 
steeply  (45°  or  more)  to  the  west.  The  slates  are  green  and  cliert}^  and 
the  quartzite  is  gray  or  white  and  novaculitic.  To  the  east  the  quartzose 
layers  jja^s  into  cherty  and  ferruginous  bands.  The  chert  bands  wedge 
out  and  then  occur  in  flat  lenticules  surrounded  by  slate.  Farther  east  the 
ledge  disappears,  but  the  ground  is  strewn  with  great  fragments  and 
bowlders  of  a  fairly  coarse-grained  calcareous  quartzite  cut  by  a  few 
quartz  veins. 

This  quartzite  is  light  gray  in  color  and  its  weathered  surface  is  pitted 

with  little  holes  marking  the  places  from  which  some  constituent,  probably 

calcite,  has  been  removed.     West  of  the  railroad  some  few  hundred  steps 

the  quartzite  is  exposed  in  place  on  the  side  of  a  little  knob  overlooking  a 

.  swamp.      Here  it  appears  to  have  a  thickness  of  at  least  50  feet. 

Although  no  rocks  other  than  those  described  occur  in  the  near  neigh- 
borhood, which  might  serve  to  determine  the  relations  of  these,  the  petro- 
graphical  character  of  the  slates  is  so  distinctly  like  that  of  the  Hanbury 
slates  elsewhere  that  no  doubt  is  felt  as  to  the  stratigraphical  position  of  the 
beds.  They  are  more  cherty  than  is  usuall}'  the  case,  but,  as  will  be  shown 
later,  they  contain  no  greater  proportion  of  cherty  material  than  is  met  with 
at  several  other  places  in  the  slate  area.  The  occurrence  is  particularly 
interesting  for  the  great  thickness  of  the  quartzite  bed. 

Under  the  microscope  the  quartzite  differs  from  the  quartzite  of  the 
Sturgeon  formation  in  containing  many  large  and  small  fragments  of  pla- 
gioclase,  orthoclase,  and  microcline.  Moreover,  its  quartz  grains  lack  the 
distinct  clastic  appearance  of  those  in  the  Sturgeon  quartzites.     The  grains 

MON  XLVI — 04 30 


466  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

seem  to  be  corroded,  and  neighboring  grains  therefore  appear  to  interlock 
b}^  irregular  sutures.  Calcite  or  dolomite  is  also  present  in  the  rock,  partly 
as  little  nests  between  the  quartz  grains  and  partly  as  a  sparse  cement.  It 
may  be  due  to  the  presence  of  this  component  that  the  quartz  gi-ains  have 
the  corroded  outlines. 

Calcareous  slates  and  dolomites. — By  the  addition  of  calcareous  material 
the  argillaceous  slates  pass  into  the  calcareous  slates.  These  sometimes 
contain  as  much  as  50  per  cent  of  calcite  or  dolomite  as  a  cement.  With 
an  increase  in  the  carbonate  the  slates  lose  their  slaty  character,  become 
more  massive,  and  finally  pass  into  beds  of  limestone  or  dolomite  measuring 
from  a  few  inches  to  20  feet  in  thickness.  On  weathered  surfaces  both  the 
dolomite  and  the  calcareous  slates  are  often  coated  with  a  skin  of  brown 
ocherous  limonite,  which  in  the  case  of  some  of  the  massive  dolomites 
reaches  a  thickness  of  an  inch  or  more.  Much  of  the  limonite  is  pseudo- 
morphous  after  siderite.  These  facts  show  that  the  dolomites  are  sideritic, 
and  that  the  siderite  has  partly  decomposed,  producing  limonite. 

When  fresh  the  calcareous  slates  are  lighter  colored  than  the  corre- 
sponding argillaceous  phases,  their  color  being  usually  some  shade  of  gray. 
They  lack  the  silvery  luster  of  the  sericitic  varieties  and  their  schistosity. 
Where  their  weathered  surfaces  are  not  incnisted  with  limonite  they  are 
pitted  with  little  pores  from  which  the  carbonate  has  been  dissolved. 

The  calcareous  slates  may  be  divided  into  two  classes:  (1)  Those  into 
which  carbonate-bearing  solutions  infiltrated,  depositing  nests  of  calcite 
and  dolomite,  and  (2)  those  in  which  these  carbonates  and  siderite  appear 
as  original  components  in  the  form  of  small  grains  and  tiny  rhombohedral 
crystals  or  groups  of  crystals.  The  first  class  includes  those  slates,  cut  by 
calcite  and  dolomite  veins,  which  are  saturated  with  carbonate  material. 
This  occurs  either  in  elongated  nests  arranged  in  lines  along  the  cleavage 
planes  or  as  a  matrix  in  winch  the  sericitic,  quartzose,  and  chloritic  compo- 
nents of  the  rock  are  embedded.  In  the  second  class  the  carbonate  appears 
to  be  the  embedded  material.  The  matrix  surrounding  the  carbonate  is  a 
fine-grained  aggregate,  with  the  composition  and  structure  of  the  argilla- 
ceous slates.  As  in  the  first  variety,  the  carbonate  is  arranged  in  lines  that 
are  parallel  to  the  cleavage. 

The  calcareous  slates  grade  into  dolomites  which  vary  in  color  through 
many  shades  of  gray  and  pink.     The  majority  are  dark-gray,  impure  varie- 


ALGONKIAN,  HANBURY  SLATE.  467 

ties,  very  different  from  the  dolomite  of  the  Raiidville  foimatioii,  while  a 
few  beds  consist  of  pink  varieties  identical  in  appearance  with  many  speci- 
mens of  the  Randville  dolomite.  In  many  cases  the  dolomites  are  closely 
associated  with  cherts  and  sometimes  with  thin  beds  of  limonite  or  other 
ferruginous  compounds.  Their  lithological  features  will  be  referred  to  at 
greater  length  in  the  discussion  of  occurrences. 

Cherts  and  ferruginous  oxides. — The  ferruginous  cherts  and  iron  oxides 
are  not  known  to  be  present  in  the  Hanbury  slate  in  large  quantity. 
Indeed,  they  are  usually  only  locally  developed  in  association  with  the 
sideritic  dolomites  and  calcareous  slates  where  these  have  been  severely 
crushed  or  folded.  The  source  of  the  iron  oxides  is  clearly  iron-bearing 
carbonate  in  the  calcareous  slates  and  the  dolomites. 

The  cherts  are  white  or  yellow  massive  rocks  Avith  a  finely  granular 
texture.  They  occur  as  thin  seams  and  veins  traversing  the  slates  and 
dolomites,  and  as  thin  beds  interlaminated  with  equally  thin  beds  or  seams 
of  hard  siliceous  and  ocherous  slates  and  with  thicker  beds  of  dolomite. 

Wherever  the  cherts  occur  there  is  usually  found  also  a  greater  or  less 
quantity  of  some  iron  oxide.  Sometimes  this  appears  as  small  veins  of 
pure  hematite  cutting  through  the  cherts,  sometimes  as  coatings  of  hema- 
tite on  the  walls  of  cracks  traversing  the  slates,  sometimes  as  small  vugs 
inclosed  in  shattered  cherts,  sometimes  as  druses  covering  the  walls  of  the 
cavities  in  an  extremely  porous  chert,  sometimes  in  distinct  bands  interlam- 
inated with  bands  of  graywacke  or  quartzite,  and  sometimes  in  the  form  of 
a  mixture  of  oxides  and  hydroxides  impregnating  slatv  material.  In  short, 
the  iron  oxides  occur  in  all  forms  characteristic  of  deposits  precijaitated 
from  percolating  waters.  The  slates  impregnated  with  ferruginous  matter 
are  naturally  dark  red  or  black.  Where  but  slightly  ferruginous  they  still 
plainly  exhibit  their  true  character.  When,  however,  the  proportion  of  the 
iron  oxides  is  large,  but  few  traces  of  the  original  slate  remain,  and  the 
rock  resembles  a  slaty  ocher  or  a  compact  siliceous  ore. 

At  several  places,  more  particularly  at  one  place  in  the  slate  area  near 
the  south  quarter  post  of  sec.  21,  T.  39  N.,  R.  28  W.,  the  banding  of  the 
material  obtained  from  a  deep  shaft  appears  on  the  weathered  surfaces  to 
be  as  even  and  as  well  defined  as  the  banding  of  the  ores  and  ferruginous 
quartzose  slates  of  the  Curry  member.  Close  inspection  of  the  hand  speci- 
mens, however,  especially  where  made  on  fresh  fracture  surfaces,  shows 


468  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

that  the  resemblance  to  the  Curry  rock  is  iUusory.  The  banded  rock  is 
mainly  a  graywacke  interlaminated  here  and  there  with  layers  of  slate.  A 
set  of  cracks  cuts  the  graywacke  parallel  to  its  bedding  planes,  and  along 
these  the  percolating  waters  found  ready  passage.  An  earthy  hematite  was 
deposited  in  the  cracks  and  in  the  rock  mass  adjacent  to  them,  thus  pro- 
ducing bands  of  ore  material  separated  by  belts  of  the  graywacke,  in  which 
there  was  little  deposition  of  ore. 

Large  deposits  of  hematite,  such  as  characterize  the  Hanbury 
formation  west  of  the  Menominee  River,  in  the  Florence,  Crystal  Falls, 
and  Iron  River  districts,  are  not  known  in  tlie  Menominee  district;  but  ore 
bodies  sufficiently  large  to  warrant  exploration  have  been  discovered  at 
several  widely  separated  localities.  These  localities  will  be  referred  to 
more  particularly  in  subsequent  pages  and  the  charactei*  of  the  cherts  and 
ores  in  each  will  be  briefly  described. 

Igneous  rocks  and  their  contact  deposits. — In  several  places  the  slaty 
series  is  intruded  by  greenstones  mainly  in  the  form  of  dikes.  The 
igneous  rocks  in  their  present  condition  are  much  altered  diabases  or 
basalts  composed  of  lu-alitized  augite  or  hornblende,  decomposed  plag'ioclase, 
and  a  considerable  quantity  of  quartz  that  is  probably  entirely  secondary. 

Tlie  slates  in  contact  with  the  igneous  rocks  are  in  many  instances 
metamorphosed  to  a  slight  extent.  Actinolite  has  developed  in  them  as 
single  long,  slender,  needles  penetrating  all  the  other  components  and  as 
radial  groups  of  needles.  A  few  large  plates  of  dark-green  chlorite  also 
occur  in  some  of  the  metamorphosed  phases  and  a  little  altered  feldspar  is 
present  in  very  irregularly  shaped  masses  forming  a  sort  of  matrix  by 
which  all  the  other  constituents  are  surrounded.  This  feldspar,  whicli  is 
now  partly  changed  to  kaolin  or  saussurite  and  is  reddened  by  ferruginous 
dust  particles,  must  have  been  infused  into  the  sedimentary  rock  from  the 
neighboring-  intrusive.  In  most  cases  the  quartz  of  the  original  slates  has 
also  suffered  considerable  change.  Its  fragmental  character  has  largely 
disappeared.  Its  contours  are  rounded,  its  peripheries  corroded,  and 
neighboring  grains  interlock.  The  fine  debris  in  the  matrix  has  entirely 
recrystallized.  In  some  specimens  calcite  is  present  in  small  quantity;  in 
others  it  occurs  in  large  quantity.  In  both  cases  it  is  apparently  an 
alteration  product  of  the  feldspar. 


ALGONKIAiN,  H ANBURY  SLATE.  469 

FOLDING  AND  SECONDARY  STRUCTURES. 

The  majoi-  folding  of  the  Hanbury  slate  corresponds  with  that  of  the 
■underlying  formations.  Along  a  north-south  cross  section  there  are  three 
major  synclines  with  east-west  axes,  the  major  anticlines  having  been 
eroded  save  at  the  ends  of  the  central  dolomite  belt  and  at  tlie  east  end 
of  the  western  area  of  Qninnesec  schist.  At  these  ^^laces  the  slates 
should  present  plunging  anticlines.  The  exposures  necessary  to  confirm 
this  inference  are  lacking.  The  north-soutli  major  folds  corresponding 
to  the  broad  north-south  folds  of  the  Randville  dolomite  are  not  easily 
recognizable.  The  slate  belts,  however,  widen  to  the  west  and  wrap 
around  both  ends  of  the  central  dolomite  area  and  around  the  east  end  of 
the  western  Qninnesec  schist  area.  There  must  be  anticlinal  arches  over 
the  dolomite  and  the  schists  with  a  synciine  between,  and  there  must  also 
exist  a  second  synciine  between  the  eastern  end  of  the  central  dolomite 
belt  and  the  Loretto  mine.  The  slates  must  likewise  pass  over  the  ore- 
bearing  beds  at  this  place  in  an  anticline  and  beneath  the  Paleozoic  beds 
to  the  east  by  another  synciine.  Thus  the  formation  must  be  affected  by 
three  broad  anticlines  and  three  broad  synclines  with  north-south  axes. 

Within  the  major  folds  the  slates  are  crowded  together  in  many  close 
minor  folds,  here  pitching  in  one  direction,  and  there  in  another.  No 
definite  system  has  been  discovered  in  the  minor  folds,  chiefly,  perhaps, 
because  outcrojjs  are  so  scarce.  In  general,  however,  the  pitch  of  these  folds 
in  the  westei'u  portion  of  tlie  district  is  to  the  west,  and  in  its  eastern 
portion  toward  the  east.  On  one  or  two  of  the  hillocks  on  which  exposures 
are  fairly  plentiful  it  was  observed,  moreover,  that,  as  a  rule,  the  little 
folds  at  the  east  ends  of  the  hillocks  pitch  to  the  west,  and  those  on  the 
west  ends  to  the  east,  at  angles  varying  between  20°  and  45°.  These 
hillocks  thus  constitute  open  cross  synclines  with  approximately  north-south 
axes,  corresponding  to  the  broad  north-south  folds  of  the  formation  as  a 
whole. 

The  east-west  minor  folds,  on  the  other  hand,  are  extremely  close 
folds.  Frequently  on  ledges  that  show  cross  sections  10  or  12  feet  across 
several  small  anticlines  or  synclines  may  be  plainly  seen,  so  closely 
compressed  that  the  dips  of  their  opposite  limbs  vary  but  a  few  degrees. 
Frequently,  too,  the  folds  are  overturned  so  that  the  dips  of  the  limbs  are 
in  the  same  direction.     On  horizontal  exposures  these  close  folds  aj-e  often 


470  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

very  difficult,  if  not  impossible,  to  detect,  so  that  in  many  cases  the  closely 
folded  beds  appear  to  be  consecutive.  The  strikes  of  the  folds  are  usually 
a  little  north  of  west,  and,  consequently,  the  strike  of  the  bedding  is 
approximately  in  the  same  direction,  and  this  is  also  the  direction  of  trend 
of  the  Menominee  trough.  Departures  from  this  strike  are  noticeable  in 
many  instances,  but  the  variations  are  not  great  except  in  a  few  restricted 
areas  where  the  pitch  due  to  cross  folding  is  marked.  Small  folds  with 
dimensions  of  an  inch  or  two  are  present  everywhere.  These  often  cause 
flutings  and  puckerings  of  the  strata  to  such  an  extent  that  even  approxi- 
mate strikes  and  dips  can  not  be  obtained.  In  some  places  lens-shaped 
deposits  of  quartz  have  been  found  between  the  layers  of  the  slate  at  the 
apices  of  the  little  anticlines  and  in  the  troughs  of  the  little  synclines. 

The  strong  north-south  compression  of  the  slate  beds,  producing  the 
close  east-west  folds,  also  impressed'  upon  all  the  weaker  members  of  the 
slate  formation  a. perfect  slaty  cleavage  with  a  nearly  east- west  strike  and 
a  dip  that  varies  but  a  few  degrees  on  either  side  of  the  vertical.  In  addi- 
tion to  this  cleavage  there  was  also  often  produced  a  set  of  fracture  planes 
or  .joints  at  right  angles  to  the  cleavage.  These  latter  intersect  the  rocks 
at  approximately  equal  intervals  of  several  inches.  In  some  places  they 
are  bordered  by  naiTOw  shear  zones  in  which  the  total  displacement  of  the 
slate  beds  is  an  inch  or  more.  On  flat  hoi'izontal  surfaces  two  sets  of  these 
joints  are  sometimes  seen  cutting  each  other  at  acute  angles,  and  about  each 
slight  faulting  has  occurred.  All  of  the  phenomena  presented  by  the  slates 
indicate  that  they  were  subjected  to  powerful  north -south  stresses  acting 
nearly  at  right  angles  to  the  axis  of  the  Menominee  trough  and  producing 
the  close  east-west  folds,  the  cleavage,  and  the  jointing;  and  that  at  the 
same  time  they  were  influenced  by  less  powerful  east-west  stresses  acting 
along  the  axis  of  the  troughs,  and  producing  the  open  north-south  cross 
folds. 

THICKNESS. 

No  approximately  correct  estimate  of  the  thickness  of  the  Hanbury 
slate  is  at  present  possible.  The  similarity  of  the  beds  and  their  reduplica- 
tion in  consequence  of  the  close  folding  render  it  impossible  to  determine 
what  proportion  of  the  apparent  thickness  of  the  formation  is  due  to  folding 
and  what  proportion  is  due  to  successive  deposits.  There  can  be  no  doubt 
that  the  Hanbury  slate  is  much  thicker  than  any  of  the  other  formations  in 


ALGONKIAN,  H ANBURY  SLATE.  471 

the  district,  but  that  it  is  as  thick  as  the  corresponding'  formation  in  the 
Penokee  district — 12,000  feet — is  not  probable.  Indeed,  it  is  extremely 
doubtful  whether  its  maximum  thickness  is  more  than  2,000  or  3,000  feet, 
though,  as  has  been  said,  this  estimate  is  not  founded  on  sufHcient  data  to 
make  it  of  nmch  value. 

RELATIONS  TO  PALEOZOIC  BEDS. 

The  relations  of  the  Hanbury  slate  to  the  underlying  Vulcan  formation, 
the  Randville  dolomite,  and  the  Archean  schists  have  already  been  fully 
discussed  (pp.  289,  365-372).  The  relations  of  the  formation  to  the  overlying 
Paleozoic  sediments  are  those  of  a  much-deformed,  closely  folded,  highly 
tilted  set  of  beds  to  a  set  of  undisturbed  horizontal  deposits  laid  down  upon 
them.  No  actual  contacts  of  the  slates  with  the  overlying  sediments  have 
been  seen,  but  from  the  nature  of  the  structural  differences  exhibited  by 
them  there  is  no  doubt  as  to  the  existence  of  a  profound  unconformity 
between  the  two.  During  the  interval  represented  by  the  break  the  Upper 
Huronian  beds  were  raised  above  the  sea,  closely  folded,  deeply  eroded, 
and  again  lowered  beneath  the  water's  surface. 

INTERESTING  LOCALITIES. 

The  most  interesting  points  at  which  to  study  the  Hanbury  slate  are 
(1)  those  at  which  the  formation  is  exhibited  in  its  typical  development, 
and  (2)  those  at  which  its  unusual  cherty  and  ferruginous  phases  occur. 
The  latter  are  of  interest  because  of  the  light  they  may  throw  on  the 
problem  of  the  origin  of  the  jaspilites  and  ores  of  the  Vulcan  formation, 
and  because  they  suggest  the  possible  presence  of  ore  deposits  in  the  slates 
like  those  in  their  western  extension  across  the  Menominee  River. 

TYPICAL   LOCALITIES. 

Exposures  of  the  Hanbury  slates  are  so  scarce  that  only  in  a  few 
places  may  more  than  one  phase  be  seen.  In  several  places,  however,  all 
the  lithological  types  of  the  formation  are  well  exhibited.  Two  such 
localities  are  described  below  and  two  others  in  which  the  slaty  phases  are 
best  shown. 

Sec.  13,  T.  40  N.,  B.  31  Tf.— The  exposures  along  both  sides  of  the 
Menominee  River  in  sec.  13,  T.  40  N.,  R.  31  "W.,  have  already  been 
referred  to  on  a  former  page  (p.  289),  in  discussing  the  relations  between 


472  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  Quinnesec  schists  and  the  Huronian  sedimentaries.  The  slates  form 
the  banks  of  the  river  and  the  bottom  of  its  channel  for  a  distance  of  about 
300  paces.  Between  the  slate  exposures  and  the  nearest  ledge  of  green 
schist,  which  is  immediately  under  the  railroad  bridge  of  the  Florence 
branch  of  the  Chicago  and  Northwestern  Railway,  is  an  interval  of  about 
150  paces  free  of  exposures  of  any  kind.  The  slates  are  cut  through  hj 
the  stream,  leaving  little  perpendicular  walls  about  8  feet  high  bordering 
both  sides  of  the  channel.  The  rocks  in  these  walls  are  silvery-gray 
sericitic  slates  with  a  well-marked  cleavage  dipping  higli  (80°)  to  the  north, 
and  a  jointing  at  right  angles  to  tliis  direction.  Their  strike  is  nearly 
east-west  across  the  stream,  the  water  of  which  flows  across  their  upturned 
edges  in  a  little  rapids. 

At  about  the  middle  of  the  exposure  on  the  Michigan  side  of  the  river 
the  slates  are  fluted  in  a  series  of  small  wave-like  folds  and  are  crossed  by 
joints  at  right  angles  to  the  general  dip  of  the  fluting.  Near  the  joint 
cracks  there  has  been  movement  in  a  narrow  shear  zone  which  has 
produced  a  distinct  schistosity  wliich  is  inclined  to  the  joints  at  angles  of 
about  60°. 

Hanhury  Hill. — Hanbury  Hill,  situated  just  south  of  Lake  Hanbury, 
furnishes  the  best  exhibition  of  the  Hanbury  slates  and  their  associated 
greenstones  found  anywhere  in  the  district.  The  hill  is  the  most  marked 
topographic  feature  within  the  slate  area.  It  rises  about  140  feet  above  the 
surrounding  plain,  its  apex  reaching  an  altitude  of  a  little  over  1,040  feet 
above  sea  level.  From  a  physiographic  point  of  view  it  is  a  monadnock, 
which  has  resisted  erosion  because  there  are  associated  with  the  soft  slates 
at  this  place  large  dikes  and  sheets  of  intrusive  basic  rocks  which  are  now 
represented  by  greenstone-schists. 

The  predominant  rocks  exposed  on  the  hill,  in  addition  to  the  green- 
stones, are  dark-gray  argillaceous  slates,  light-gray  calcareous  slates,  gray- 
wackes,  and  quartzites.  These  are  folded  in  a  most  intricate  manner  in  the 
central  portion  of  the  elevation,  but  on  its  east  side  the  pitch  of  the  folds  is 
uniformlv  toward  the  west  and  on  the  west  side  toward  the  east.     Where 

4/ 

folding  it  not  pronounced  the  strike  of  the  beds  is  about  N.  78°  W.,  but 
there  are  many  places  where  the  strike  departs  widely  from  this,  especially 
on  the  higher  points  of  the  hill.  In  one  place  near  the  west  end  of  the  top 
of  the  hill  a  strike  was  measured  and  found  to  be  nearly  north-south.     At 


ALGONKIAN,  HANBURY  SLATE.  473 

this  place  the  foklmg  is  very  distinct.  The  httle  folds,  where  the  proper 
observations  conld  be  made,  were  found  to  pitch  east  at  20°  and  to  strike 
N.  85°  W.  In  other  portions  of  the  hill  near  its  west  end  the  folds  are 
/ery  close.  Their  axes  usually  pitch  east  at  angles  varying  between  20° 
and  45°,  but  in  a  few  instances  the  angle  of  pitch  is  much  higher,  reaching 
90°  in  a  few  cases.  The  general  dijj  of  the  beds  in  the  hill  approximates 
70°  S.,  showing  that  the  folds  are  frequently  ovei'turned  to  the  north,  but 
of  course  dips  of  all  angles  and  in  all  directions  are  met  with,  as  uuist  be 
the  case  in  a  series  of  folded  beds.  Northern  dips  are,  however,  rare,  aiid 
where  observed  they  are  always  much  steeper  than  the  southern  ones. 

All  the  beds  are  crossed  by  a  schistosity  that  strikes  about  N.  75°  W. 
and  dips  from  80°  S.  to  90°,  irrespective  of  the  folding.  It  therefore  some- 
times corresponds  with  the  bedding  of  the  slates,  but  more  frequently  the 
two  structures  are  discordant. 

The  greenstone-schists  are  limited  almost  exclusively  to  the  northern 
23art  of  the  hill,  although  a  few  ledges  have  been  observed  on  its  south 
side,  especially  where  the  hill  is  widest,  i.  e.,  near  the  section  line  between 
sees.  15  and  16.  The  relation  of  the  schists  to  the  surrounding  slates  is 
not  always  easy  to  ascertain.  In  most  instances  the  greenstone  apj^ears  to 
intrude  the  bedded  series  in  the  form  of  large  dikes,  but  in  the  northwest 
part  of  the  hill  the  igneous  rock  appears  to  underlie  slates,  both  on  the 
north  and  on  the  south  sides  of  a  minor  elevation;  consequentlv  tlie  rock 
in  this  case  may  be  an  intruded  sill.  In  all  cases  the  greenstone  is  strongly 
schistose  in  the  same  direction  as  the  neighboring  slates.  In  composition 
it  is  an  aggregate  of  fibrous  hornblende  and  the  decomposition  products  of 
feldspar.  None  of  the  original  constituents  remain.  In  structure  the  rock 
was  apparently  granular,  although  the  presence  of  small  white  spots  sprink- 
led over  the  dark-green  weathered  surfaces  oi  some  of  the  schists  may 
indicate  that  these  were  originally  porphyritic.  The  greenstone  occupies 
some  of  the  higher  peaks  of  the  hill  and  forms  a  little  cliff  about  20  feet 
high  with  a  northern  face  overhanging  the  lake. 

The  various  phases  of  the  slates,  the  quartzites,  and  the  graywackes 
are  interbedded.  The  quartzites  and  gi'aywackes  are  usually  in  compara,- 
tively  thin  beds,  but  in  one  case  at  least  a  quartzite  bed  measures  20  feet 
in  width,  These  quartzites  are  nearly  all  calcareous,  and  gradation  phases 
between  them  and  the  calcareous  slates  or  impure  dolomites  are  common. 


474  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

The  slates,  as  before  stated,  predominate  over  all  other  rocks.     They  form 
not  only  thicker  beds  but  more  numerous  ones. 

The  calcareous  phases  occupy  distinct  horizons  toward  the  north  side 
of  the  hill  They  are  interbedded  with  the  argillaceous  phases,  but  the 
former  greatly  predominate.  The  argillaceous  phases,  on  the  other  hand, 
are  moi-e  common  to  the  south.  Near  the  center  of  the  hill  thin  beds  of 
the  cfilcareous  slates  may  alternate  with  the  argillaceous  ones,  but  farther 
south  on  its  southern  slope  the  calcareous  forms  are  entirely  lacking.  Here 
the  gray  slates  exclude  all  other  rocks.  While  the  exact  stratigraphical 
position  of  the  calcareous  slates  is  not  certainly  known,  on  account  of  the 
complicated  folding  of  the  series,  it  is  nevertheless  believed  that,  together 
with  the  graywackes  and  the  quartzites,  they  occupy  low  horizons  and  that 
the  argillaceous  phases  occur  above  them. 

Under  the  microscope  the  gray  and  black  argillaceous  slates  are  seen 
to  be  typical  clay  slates,  composed  of  fine  quartz  grains,  spicules  of  chlorite 
and  sericite,  flakes  of  kaolin  and  the  usual  accessory  particles.  Some  of 
the  quartz  is  plainly  in  fragmental  grains,  but  most  of  it  has  been  recrys- 
tallized.  Near  the  contacts  with  the  greenstones  a  little  brown  biotite  has 
been  developed  in  them,  otherwise  the  contact  phases  are  not  essentially 
different  from  the  normal  ones.  Where  most  contorted,  both  normal  and 
contact  varieties,  more  particularly  the  latter,  are  traversed  by  an  intricate 
system  of  veins  and  veinlets  of  quartz. 

The  argillaceous  slates  pass  into  the  quartzites  by  increase  in  their 
quartzose  components.  The  most  distinct  quartzites  are  dark-gray  or  black 
varieties  that  are  usually  covered  on  their  weathered  surfaces  by  a  crust  of 
brown,  earthy  limonitic  material  that  indicates  the  presence  of  siderite  in 
the  fresher  portions  of  the  rock.  Here  and  there  they  are  cut  by  quartz 
veins,  and  near  contacts  with  the  greenstone  they  are  gashed  and  jointed 
into  polygonal  blocks,  many  of  which  are  bounded  by  curved  surfaces. 
The  quartzites  are  much  less  schistose  than  the  other  rocks  in  the  hill,  but 
all  specimens  show  some  indications  of  the  structure.  Under  the  microscope 
the  rocks  present  two  types.  In  both  types  the  quartz  grains  have  more  or 
less  ragged  outlines  in  place  of  the  sharp  ones  characteristic  of  clastic 
quartz,  as  though  they  had  been  partly  dissolved  and  new  quartz  had  added 
itself  to  the  imdissolved  nuclei.  The  two  types  differ  in  the  amounts  and 
character  of  their  matrices.     In  one  type  the  matrix  is  in  comparatively 


ALGONKIAN,  HANBURY  SLATE.  475 

large  quantity,  constituting  perhaps  50  per  cent  of  the  rock.  It  has  the 
usual  character  of  the  matrix  of  the  argillaceous  slates,  except  that  it 
contains  a  great  deal  of  a  light-brown  carbonate  in  small  grains  and  groups 
of  grains,  and  in  large  pieces  that  look  as  though  they  might  be  pseudo- 
morphs  after  some  other  mineral,  or  the  fillings  of  pores  or  cavities.  In  the 
second  type  the  matrix  is  sparse.  It  consists  of  an  occasional  plate  of 
chlorite  and  sericite  and  many  small  rhombohedra  of  a  yellowish-brown 
carbonate  that  is  locally  changed  into  limonite.  The  carbonate  crystals  in 
this  type  of  quartzite  are  plainly  ferruginous.  The  carbonate  in  the  first 
type  seems  to  be  partly  a  ferruginous  carbonate  and  partly  calcite  or 
dolomite. 

The  calcareous  slates  diff"er  from  the  quartzites  mainly  in  the  absence 
of  the  large  quartz  grains  and  the  presence  of  more  abundant  carbonate. 
They  are  essentially  like  the  matrices  of  the  quartzites  of  the  first  type, 
except  that  they  contain  even  more  of  the  carbonate.  This  mineral  often 
makes  up  by  far  the  greater  portion  of  the  rock.  It  is  an  a,ggregate  of 
granules,  many  of  which  liave  a  rhombohedral  habit.  When  the  texture  is 
extremely  fine  the  rocks  resemble  slates  more  than  they  do  quartzites; 
when  coarser  they  graduate  into  the  latter  rocks. 

Sturrjeon  Mills. — East  and  southeast  of  Sturgeon  Mills,  in  sec.  13,  T. 
39  N.,  R.  29  W.,  are  several  small  knobs  of  black  slates  that  are  easily 
accessible  from  the  railroad  track  east  of  Sturgeon  Mills  station.  On  the 
ea.st  side  of  the  mill  pond  (see  map,  PI.  XLI)  the  slates  form  a  considerable 
knoll  in  which  the  most  typical  phase  of  the  black  variety  is  beautifully 
exposed.  The  rocks  are  dense  and  homogeneous  and  are  crossed  by  a 
well-marked  cleavage  that  is  vertical.  No  bedding  is  noticeable.  Farther 
south,  alongside  the  railroad  track,  the  same  rock  occurs  in  two  flat  ledges 
with  a  vertical  schistosity  striking  east-west.  In  the  northern  ledge  the 
bedding  is  much  contorted,  the  little  folds  in  every  instance  pitching  about 
55°  E. 

On  or  near  the  banks  of  the  river  are  other  ledges  in  which  slates  and 
quartzites  are  interlaminated.  Here,  too,  the  bedding  is  much  folded, 
and  again  the  folds  pitch  to  the  east,  the  angle  of  pitch  being  between  30° 
and  40°.  Greenstones  are  associated  with  the  slates  in  the  southern  ledges, 
and  in  several  instances  the  knobs  rising  above  the  plain  expose  only  the 
intrusive  rock. 


476  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

Sees.  29  and  30,  T.  39  K,  R.  28  W.—ln  the  central  portion  of  sec.  29 
and  the  eastern  part  of  sec.  30,  in  T.  39  X.,  R.  28  W.,  the  slates  of  the  Han- 
bury  formation  are  well  exposed  in  a  nunilier  of  little  knobs  and  flat  ledges 
on  both  sides  of  the  road  running  southwest  from  Waucedah.  In  sec.  30 
the  slates  are  calcareous  in  part,  and  in  part  sericitic,  and  ai-e  associated  with 
schistose  greenstones  of  the  usual  types.  In  nearly  all  the  ledges  folding- 
is  ver^-  apparent.  The  axes  of  the  sharp,  close  folds  strike  N.  75°  W.  and 
pitch  15"  E.  The  slates  are  also  schistose,  with  the  schistosity  striking 
parallel  to  the  axes  of  the  folds,  and  consequently  in  some  places  across  the 
bedding,  and  in  other  places  parallel  with  it.  Farther  east,  in  sec.  29,  the 
gray  argillaceous  slates  predominate,  although  a  few  beds  of  calcareous 
slates  are  interbedded  with  them.  Here,  too,  the  rocks  are  contorted  and 
schistose.  The  schistosity  strikes  east-west,  crossing  the  immerous  little 
folds  at  inclined  angles.  The  strike  of  the  axes  of  the  folds  is  about  N.  45° 
W.  and  their  pitch  is  to  the  east. 

LOCALITIES    AT    WHICH    CHERTS    OCCUR. 

The  second  group  of  localities  within  the  Hanl3ury  area  that  are  of 
special  interest  are  those  in  which  cherty  and  ferruginous  rocks  occur. 
Comparatively  only  a  few  of  these  ate  known  at  present,  all  of  which  are 
briefly  referred  to  below. 

Sec.  15,  T.  40  N.,  B.  30  W. — In  the  southeast  quarter  of  the  southwest 
quarter  of  sec.  15,  T.  40  N.,  R.  30  W.,  near  the  point  where  the  road  crosses 
the  little  stream  flowing  north,  are  two  deep  test  pits  or  exploring  shafts, 
from  which  a  large  quantity  of  material  was  taken  many  years  ago.  The 
rocks  on  the  dump  piles  are  much  weathered,  but  there  can  be  distinguished 
among  them  various  slates,  cherts,  and  lean  ores.  At  the  pit  about  200 
paces  west  of  the  stream  the  material  on  the  dump  is  principally  a  sheared 
pink  ferruginous  slate,  containing  considerable  talc  or  serpentine  along  the 
shearing  planes  between  the  lamina^.  It  looks  extremely  like  the  talcose 
slates  lying  between  the  Randville  dolomite  and  the  base  of  the  Vidcan 
l)eds.  The  other  pit  is  about  200  paces  south  of  the  same  stream.  Here 
the  principal  material  on  the  dump  is  a  ferruginous  slate  not  very  different 
from  that  at  the  western  pit.  In  addition  to  this,  however,  there  are  many 
fragments  of  a  red  and  gray  cherty  quartzite,  some  fragments  of  a  well- 
characterized  jasper,  and  a  few  pieces  of  a  very  lieavy  brecciated  jasper 


ALGONKIAN,  HANBURY  SLATE.  477 

in  wliich  the  fragments  are  cemeuted  by  a  porous  crystallized  mass  of 
hematite.  The  cherts  or  jaspers  are  very  much  more  like  some  varieties 
in  the  Vulcan  formation  than  like  those  in  the  Haubury  slates.  There  are 
no  exposures  of  any  kind  in  the  vicinity  of  the  pits,  and  consequently  there 
is  no  way  of  learning  what  the  relations  of  these  rocks  are  to  those  north 
and  south. 

The  nearest  rocks  outcropping  to  the  north  are  the  Quinnesec  schists 
of  the  western  area.  Those  to  the  south  are  the  sandstones  covering-  the 
hill  north  of  the  Cuff  mine.  If,  as  has  been  reported,  a  drill  j)ut  down  in 
the  northeast  corner  of  sec.  21  penetrated  the  Randville  dolomite,  then  the 
dolomite  is  but  a  short  distance  south  of  the  southern  pit.  If  this  latter 
condition  is  true,  the  jasper  and  ores  reached  by  the  pits  may  belong  in  the 
Vulcan  formation  and  the  talcose  slates  may  be  the  slates  on  the  top  of  the 
Randville  formation.  In  this  event  there  would  be  a  narrow  syucline  of 
Vulcan  beds  between  the  Quinnesec  schists  on  the  north  and  the  Randville 
dolomite  on  the  south.  There  is  no  possible  method  at  present  of  deciding 
whether  this  view  of  the  case  is  correct  or  not,  and  so,  in  the  interests  of 
conservatism,  the  jaspers  and  ores  are  regai-ded  as  poi-tions  of  the  Hanbury 
formation  and  the  general  map  (PI.  IX)  is  colored  accordingly. 

Sec.  11,  T.  39  N.,  R.  30  W. — Another  place  within  the  area  of  the 
Hanbur}'  slate  at  AA'hich  cherts  are  found  is  near  the  center  of  sec,  11,  T. 
39  N.,  R.  30  W.,  on  the  top  of  the  terrace  just  west  of  the  point  where 
the  railroad  to  Little  Quinnesec  Falls  crosses  the  highway  running  from 
Quinnesec  to  the  same  point.  Here  there  are  several  exposures  of  typical 
Hanbury  slates  and  several  test  pits.  The  pit  nearest  the  railroad  is  in  the 
normal  clay  slates  of  the  formation.  These  strike  east-west,  as  shown  by 
exposures  near  by.  About  150  paces  east  and  150  or  200  paces  north  is 
another  pit,  south  of  a  large  ledge  of  slates  striking  also  east-west.  The 
slate  is  strongly  schistose,  and  this  structure  strikes  in  the  same  direction. 
Its  dip  is  vertical. 

On  the  dump  of  the  pits  are  rocks  some  of  which  are  unlike  anything 
else  seen  in  the  district.  A  few  of  the  pieces  seem  to  be  a  network  of 
quartz  veins,  with  its  meshes  filled  b)'  a  mass  of  hematite  and  chlorite. 
A  few  others  are  slate.  The  greatest  number  consist  of  a  streaked  and 
mottled  red  and  dark-green  chert.  The  dark  portion  has  the  texture  and 
the  general  appearance   of  flint.     The  red  portion  differs  from  jasper  in 


478  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

ha^dng■  a  duller  luster.  Both  the  red  and  the  green  portions  are  composed 
principally  of  a  very  fine-grained  crystalline  aggregate  of  quartz,  but  the 
former  contains,  in  addition,  a  large  quantity  of  hematite  and  the  latter  a 
larg'e  amount  of  chlorite.  The  hematite  is  in  small  granules  between  the 
quartz  grains  and  the  chlorite  is  in  streaks  forming  a  matrix  in  which 
the  quartz  grains  are  embedded.  Here  and  there  a  quartz  vein  traverses 
the  chert,  and  the  rock  is  moreover  incipiently  schistose.  The  near 
proximity  of  the  slate  ledges  to  the  pit  showing  these  cherts  would  appear 
to  indicate  that  these  rocks  were  formed  in  some  vein-like  crevice,  but  of 
com-se  no  proof  of  this  conclusion  is  at  hand.  The  cherts,  however,  are 
clearly  in  the  Hanbury  slates. 

Southeast  quarter  of  sec.  7  and  southwest  quarter  of  sec.  8,  T.  39  N.,  R. 
29  W. — West  and  a  little  north  of  Hanbury  Hill,  i.  e.,  nearly  on  the  general 
strike  of  the  bedded  rocks  forming  this  elevation,  is  a  little  hillock  on  which 
are  exposed  not  only  the  siliceous  and  calcai-eous  forms  of  the  Hanbury 
slates,  but  also  dolomites  and  cherts  better  developed  than  anywhere 
else  in  the  Hanbury  formation.  In  the  southeast  quarter  of  sec.  7  the 
rocks  form  a  distinct  hill  80  feet  high,  overlooking  a  swamp  which 
lies  to  the  north,  east,  and  west.  On  the  top  of  the  hillock  the  various 
slaty  phases  of  the  formation  are  well  exposed  in  a  complicated  series  of 
small  folds.  Between  the  slate  layers  there  is  occasionally  a  thin 
layer  of  coarse  grit  or  conglomerate,  containing  granite,  chert,  and 
quartz  pebbles,  and  in  the  trough  of  some  of  the  folds  the  slates  are 
brecciated.  In  some  places  the  rocks  are  cut  by  ramifying  veins  of  white 
quartz,  but  usually  veins  are  absent.  The  bedding  of  the  slates  in  the 
western  part  of  the  hill  strikes  fairly  uniformly  N.  65°  to  75°,  but  the  dips 
varv  from  63°  S.  to  65°  N.,  indicating  the  presence  of  a  synchne.  Farther 
east  the  bedding  is  much  more  contorted  and  small  folds  are  numerous. 
Moreover,  in  some  cases  a  few  of  the  layers  constituting  the  larger  folds 
are  folded  within  themselves  into  minute  crinkles  and  crumplings.  Near 
the  east  end  of  the  hillock  the  little  folds  are  well  enough  defined  to  enable 
one  in  several  instances  to  determine  the  direction  of  their  pitch.  In  one 
case  noted  the  pitch  of  a  small  fold  near  the  center  of  the  elevation  was 
found  to  be  east  at  20°  to  30°.  Farther  east  the  pitch  is  almost  uniformly 
to  th^  west  at  widely  difi'erent  angles.  This  hill,  thus,  like  Hanbury  Hill, 
is  a  synclinorium  with  the  axis  of  the  fold  transverse  to  the  axis  of  the 


ALGONKIAN,  HANBURY  SLATE.  479 

elevation.     Its  presence  as  a  hill  is  undoubtedly  due  to  the  close  folding 
to  which  its  rocks  have  been  subjected  and  their  consequent  compactness. 

All  the  slates,  whether  sharply  folded  or  not,  are  markedly  schistose,  but 
the  direction  of  the  schistosity  is  uniformly  N.  80°  to  85°  W.  and  its  dip  is 
75°  to  80°  S.  Thus  the  secondary  structure  is  inclined  to  the  bedding  at 
all  angles.  It  is  parallel  with  the  same  structure  in  the  slates  of  Hanbury 
Hill,  and  departs  only  slightly  in  direction  from  the  corresponding  structure 
observed  in  nearly  all  the  sedimentary  rocks  of  the  entire  district.  Hence 
this  structure  is  not  of  local  origin,  but  is  probably  connected  with  some 
general  cause  which  was  active  throughout  the  entire  Menominee  trough. 
The  only  general  cause  capable  of  producing  the  effect  was  that  which  at 
the  same  time  produced  the  major  folding  of  the  district  and  gave  rise  to 
the  great  synclinorium  that  constitutes  the  Menominee  trough. 

Nearly  all  the  slates  composing  the  hill  contain  iron  carbonate  to  some 
extent,  as  is  shown  by  the  almost  universal  existence  of  a  brown,  earthy 
limonitic  weathering  ci'ust.  On  its  north  slope  the  carbonate  is  especially 
abundant,  some  of  the  beds  consisting  of  a  well-characterized  ferruginous 
limestone  10  feet  or  more  thick.  This  limestone  is  dark  gray  in  color  and 
finely  granular,  and  is  covered  by  a  limonitic  skin  or  crust  one-tenth  inch 
in  thickness.  Under  the  microscope  can  be  detected  a  few  grains  of  quartz, 
a  number  of  small  plates  of  brown  mica,  an  occasional  flake  of  muscovite, 
and  a  few  spicules  of  kaolin.  The  major  portion  of  the  section  consists  of 
an  intricately  interlocking  mass  of  carbonate  and  crystallized  quartz. 

An  analysis  of  one  of  the  best  specimens  of  the  ferruginous  limestones 
from  this  place  was  made  by  Mr.  George  Steiger,  of  the  Survey  laboratory, 
with  a  view  to  the  determination  of  the  nature  of  the  cementing  carbonate 


480  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Analyais  of  fer'ruginous  dolomite  in  Hanhury  formation. 


li 

Entire 
rock. 

Soluble  in 
HCl(dil.). 

SiO, 

36.71 

5.34 

.35 

3.37 

10.78 

15. 11 

.12 

2.40 

.55 

1.61 

.27 

23.22 

.05 

.23 

} 

2.28 

AI2O3 

1.27 

FejOa 

FeO    .. 

3.61 

MgO  ..                                                    

8.83 

CaO.                                                 

15. 20 

Na^O.                             .                  

K2O                                                   

H,0  at  105° .                             

H,( )  above  105°                        

TiOj   .                                           .     - 

CO2  .       -              -   - . 

P,0=.     ..                

MnO  ....                             .              .... 

Total 

100. 11 

The  soluble  portion  includes  tlie  cai'bonates  aiid  a  small  portion  of 
some  aluminous  silicate.  If  all  the  iron,  magnesia,  and  lime  are  assumed 
to  be  in  the  form  of  carbonates  the  proportions  of  these  in  the  rock  are  5.43 
FeCOg,  18.54  MgCOg,  and  27.15  CaCOg,  which  require  the  presence  of 
23.72  per  centCOg.  The  total  amount  of  the  carbonate  present  must  be 
about  51  per  cent  of  the  entire  rock  and  its  composition  must  be  about 
as  follows:  FeCOg,  4|  MgCOg,  5|  CaCOg — or  the  carbonate  is  a  dolomite 
in  which  about  17  per  cent  of  the  MgCOg  is  replaced  by  FeCOg. 

In  some  places  the  limestone  bears  layers  of  chert  several  inches  wide. 
This  chert  is  a  dark-gray  variety  clouded  with  irregular  patches  having  a 
light-gray  or  white  color  and  marked  by  bedding  lines.  In  some  places 
the  chert  grades  on  both  sides  into  the  limestone.  In  others  it  forms  a 
distinct  band  separated  from  the  limestone  by  a  very  sharp  line.  In  the 
latter  cases  the  siliceous  rock  appears  to  occupy  a  fissure  and  to  partake 
somewhat  of  the  nature  of  a  vein.  In  both  cases  the  composition  and 
structure  of  the  chert  are  simple.  The  major  part  of  those  pliases  that 
are  most  intimately  related  to  the  limestone  is  an  aggregate  of  finely 
granular,  interlocking  silica.  In  this  there  are  embedded  abundant  little 
rhombohedra  of  a  light-yellow  carbonate,  probably  siderite,  an  occasional 


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ALGONKIAN,  HANBURY  SLATE.  481 

grain  of  hematite  or  magnetite,  and  a  few  flakes  of  biotite.  The  bedding 
observed  in  the  banded  specimen  is  due  to  the  greater  richness  in  carbonate 
of  some  portions  of  the  sections  than  others;  the  darker  bands  containing  a 
greater  proportion  of  carbonate  and  the  Hghter  ones  a  greater  excess  of 
quartz.  Tiny  quartz  veins  intersect  the  rock,  sometimes  forming  a  compli- 
cated network  traversing  the  thin  sections  in  all  directions.  The  quartz  in 
these  veins  is  much  coarser  grained  than  that  in  the  mass  of  the  chert,  and 
through  it  are  interspersed  little  nests  of  calcite  or  other  carbonate,  streaks  of 
a  black  substance  that  may  be  carbonaceous,  and  a  few  wisps  of  muscovite. 
The  carbonate  is  usually  near  the  walls  of  the  vein  and  frequently  when  in 
this  position  it  occurs  in  rhombohedra.  Those  varieties  of  the  chert  that 
are  distinctly  separated  from  the  limestone,  and  that  have  been  said  to  be 
vein-like  in  character,  diff'er  from  the  cherts  just  described  in  being  almost 
free  from  carbonate  except  on  the  selvages  of  veins.  In  many  places  the 
slates  near  the  chert  bands  are  highly  ferruginous,  and  in  one  or  two 
instances  distinct  veins  of  hematite  can  be  seen  penetrating  them. 

About  a  quarter  of  a  mile  east  of  the  east  end  of  the  hill  the  same 
kinds  of  rocks  outcrop  in  little  ledges  scattered  through  the  swamp.  Black 
slates,  quartzite,  and  impure  limestones  occur  interbedded  with  one  another 
in  such  a  way  as  to  show  that  the  general  strike  is  N.  85°  K.  and  the  diji 
about  55°  S.,  but  the  beds  are  affected  by  minor  folding,  which  naturally 
causes  many  departm-es  from  these  directions  in  both  strike  and  dip.  In 
the  midst  of  the  slate  outcrops  is  one  of  greenstone-schist,  in  which  the 
schistosity  is  parallel  to  the  cleavage  in  the  slates,  which,  of  course,  is  not 
always  coincident  with  the  bedding  in  these  rocks. 

Iron  Hill,  southeast  quarter  of  sec.  32,  T.  40  N.,  E.  29  W. — Near  Iron 
Hill,  in  the  southeast  quarter  of  sec.  32  and  the  adjoining  portion  of  sec.  33, 
T.  40  N.,  R.  29  W.,  is  the  most  extensive  exhibition  of  ores  and  cherts  seen 
anywhere  in  the  Hanbury  slate  area.  The  ledges  and  pits  in  which  they 
are  exposed  are  dotted  over  a  plain  lying  south  and  east  of  the  end  of  the 
central  dolomite  belt,  from  which  they  are  separated  by  a  naiTow  swamp 
(see  PI.  XLII).  The  dolomite  has  been  described  on  a  previous  page. 
The  fact  that  a  drill  hole  cutting  under  the  pits  along  the  east  line  of  the 
section  encountered  only  gray  slates,  like  the  typical  clay  slates  of  Hanbury 
Hill,  indicates  conclusively  that  none  of  the  cherts  and  ores  are  in  the 
Vulcan  formation. 

MON  XLVI — 04 31 


482  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

On  tlie  little  terrace  south  of  the  swamp,  and  hence  south  of  the  dolo- 
mite ridge,  are  numerous  outcrops  of  well-defined  slaty  I'ocks  striking  about 
N.  70°  W.  and  dipping  approximately  70°  S.  Some  of  these  are  clay  slates, 
others  are  graywackes,  and  others  are  impure  quartzites.  Most  of  the 
slates  are  like  the  argillaceous  Hanbury  slates,  but  some  of  them  are 
slightly  ferruginized.  Graphitic  varieties  have  also  been  met  with  in  test 
pits  sunk  in  this  portion  of  the  area,  and  here,  as  elsewhere,  they  are 
associated  with  heavily  ferruginous  beds.  In  one  pit  a  fairly  good  lean  ore 
was  encouniered. 

North  of  the  dolomite  exposures,  near  the  north  quarter  post  between 
sees.  32  and  33,  are  three  or  four  deep  shafts  and  a  tunnel  leading  from  the 
bottom  of  one  of  them  to  the  side  of  the  hill  on  which  they  are  situated. 
These  shafts  are  all  in  sandstone.  A  large  quantity  of  ocher  is  found  on 
their  dumps,  but  this  it  is  believed  must  have  come  from  a  ferruginous  bed 
at  the  base  of  the  sandstone.  Indeed,  on  some  of  the  dumps  pieces  of  con- 
glomerate were  seen  that  resemble  strongly  the  ore  conglomerate  found  at 
the  base  of  the  sandstone  at  many  places  within  the  district. 

The  pits  and  shafts  southeast  of  the  dolomite  bluffs  are  plainly  in  a 
heavily  ferruginized  zone.  They  are  at  the  base  of  a  high  hill  on  Avhich  no 
exposures  have  been  found,  but  which  is  probably  composed  mainly  of  the 
Lake  Superior  sandstone.  The  pits  have  disclosed  a  great  variety  of  rocks. 
Red  ferruginous  schistose  slates  predominate,  but  in  addition  to  these  there 
ai-e  also  on  the  dump  heaps  graphite-slates,  cherts,  thin  beds  of  hematite, 
interbanded  cherts  and  ores,  and  a  few  specimens  of  conglomerate.  The 
latter  is  from  a  thin  bed  interlaminated  with  slates. 

In  places  the  slates  approach  graywackes  in  composition  and  structure, 
and  in  other  places  they  approach  quartzites.  In  some  places  shearing  has 
been  so  severe  as  to  produce  fissility.  The  slates  nearly  all  contain  visible 
quartz  grains.  On  fracture  surfaces  their  original  color  can  be  seen  to  be 
green.  Their  present  red  color  is  due  to  a  stain  that  started  along  the  fis- 
sility planes  and  extended  inward  from  these.  In  composition  the  slates  of 
this  kind  are  very  near  to  graywacke.  Their  quartz  grains  are  often 
crushed  into  mosaics  or  mashed  into  long,  flat  lenses.  These  are  embedded 
In  a  schistose  aggregate  of  chlorite,  muscovite,  and  crystallized  quartz.  The 
brown  stain  is  due  to  the  decomposition  of  the  micaceous  constituents  and 
the  development  within  them  of  limonite  and  hematite.     Others  of  the  red 


ALGONKIAN,  HAi^BURY  SLATE.  483 

slates  contain  considerable  dolomite.  These  on  a  fresh  fracture  are  light- 
yellowish  gray.  They  are  schistose  and  stained  in  the  same  manner  as  are 
the  quartzose  slates. 

The  cherts  and  ores  are  naturally  the  most  interesting  of  the  rocks 
encountered  in  the  explorations.  Indeed  they  look  so  promising  in  a 
mimber  of  instances  that  the  general  view  as  to  the  existence  of  a  narrow 
belt  of  the  Vulcan  formation  at  this  place  is  not  to  be  wondered  at.  How- 
ever, the  cherts  are  all  sandy  textured  and  the  ores  are  very  dense,  hard, 
brownish-red  varieties  unlike  anything  seen  in  the  Vulcan  beds.  Most  of 
them  are  also  porous.  In  some  specimens  the  pores  are  little,  irregularly 
shaped,  vug-like  cavities,  lined  with  tiny  hematite  druses.  In  other  speci- 
mens narrow,  crack -like  cavities,  with  druse-covered  walls  run  through  the 
centers  of  the  bands  as  do  the  longitudinal  cavities  so  often  seen  in  veins. 
All  the  ore  layers  are  minutely  banded  and  many  of  them  are  divided 
longitudinally  into  two  or  more  parts  by  very  fine  lines,  as  though  the  ore 
material  had  grown  from  both  sides  of  the  band  inward  until  the  opjDOsite 
portions  joined.  The  only  conclusion  as  to  the  origin  of  the  ore  that  can 
bie  reached  from  a  study  of  the  fragments  thrown  out  on  the  dumps  is  that 
they  are  vein  fillings  in  a  fragmental  rock  which  has  been  partly  silicified, 
and  which,  therefore,  has  lost  some  of  its  fragmental  features.  Some  of 
the  siliceous  bands  associated  with  the  ores  are  distinct  cherts,  but  these: 
may  be  veins.  All  the  cherts  and  ores  are  jointed,  and  along  some  of  the 
joints  slight  faulting  has  taken  place. 

Again,  there  is  no  opportunity  to  study  the  relations  between  the 
difi"erent  rocks  because  of  the  impossibility  of  seeing  them  in  place.  It 
can  scarcely  be  doubted,  however,  that  the  jointing  and  ferruginization  of 
the  beds  is  connected  in  some  way  with  the  folding  that  terminated  the 
central  dolomite  belt. 

Sec.  17,  T.  39  N.,  R.  29  W. — In  about  the  center  of  the  southeast 
quarter  of  the  northeast  quarter  of  sec.  17,  T.  39  N.,  R.  2!)  W.,  several  test 
pits  have  been  put  down  in  low  ground  near  a  swamp.  Most  of  the  pits 
have  exposed  the  normal  black  siliceous  slates  of  the  Hanbury  formation 
but  a  few  of  them,  apparently  along  a  crushed  zone  in  the  slates,  have 
yielded  a  red,  2:)orous  mass  of  hematite  and  chert  that  might  be  regarded  as 
a  lean  ore.  On  the  dumps  of  several  other  pits  fragments  of  a  brecciated 
chert  are  also  noticed.     In  these  the  cement  is  a  red,  earthy  hematite,  and 


484  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

the  fragments  are  small  angular  pieces  of  light-gi-aj^  chert,  very  similar  to 
the  chert  on  the  hill  in  sec.  7  of  the  same  township.  The  relations  of  the 
cherts  and  ore  to  the  slates  are  not  known.  No  exposures  are  visible  in 
the  vicinity,  and  the  ^jits  are  now  partially  filled  with  dt'bris.  The  location 
is  referred  to  simply  because  it  is  one  of  the  places  within  the  Hanbury 
slate  area  at  which  cherts  have  been  found. 

Northwest  quarter  of  sec.  26,  T.  39  K.,  B.  29  W. — The  only  place  near 
the  southern  Quinnesec  schists  at  which  cherts  and  ferruginous  beds  have 
been  seen  is  in  the  southwest  quarter  of  the  northwest  quarter  of  sec.  26, 
T.  39  N.,  R.  29  W.,  near  Sturgeon  Falls,  on  the  Menominee  River.  On  the 
north  side  of  a  little  hillock  not  more  than  200  feet  north  of  the  State  road 
(see  map,  fig.  22)  running  east  from  the  New  York  farm  are  exposures  of 
fissile  slates  containing  layers  of  white,  gray,  and  pink  chert,  and  bands  of 
dense  black  and  dark-purple  ores.  The  rocks  are  jointed,  and  in  the  joint 
cracks  are  often  thin  deposits  of  hematite.  Some  of  the  slates  are  graphitic. 
Northeast  of  this  again,  at  a  distance  of  about  300  feet,  is  another  very 
similar  ledge  on  the  escarpment  of  a  terrace,  and  this  deflects  the  compass 
needle  to  a  very  noticeable  extent.  Still  farther  north,  about  250  paces 
iiorth  of  the  last-mentioned  ledge,  is  a  third  low  ledge  in  which  the  rocks 
are  plainly  distinctly  fissile  slates  interbedded  with  bands  of  chert.  In  this 
ledge  the  beds  are  contorted.  In  all  these  cases  the  slates  are  undoubted 
members  of  the  Hanbury  formation,  and  the  cherts  and  ores  are  secondary 
deposits. 

Se  :  21,  T.  39  N.,  B.  2S  IF.— In  the  center  of  the  south  half  of  sec.  21, 
T.  3;j  N.,  R.  28  W.,  is  another  group  of  pits  which  show  the  presence  of 
ferruginous  bands  in  the  slates.  The  pits  are  comparatively  old,  but 
quartzites,  graywackes,  and  slates  can  be  recognized  on  their  dumps.  All 
the  rocks  are  more  or  less  ferruginized,  and  some  of  the  slate  presents  the 
appearance  of  a  very  lean  banded  ore.  Reference  has  already  been  made 
to  this  ore-like  slate  in  another  place  (p.  467).  The  relations  of  the 
different  rocks  to  one  another  are  not  known.  There  is  little  doubt,  how- 
.ever,  as  to  their  being  a  part  of  the  Hanbury  formation. 

Sec.  19,  T.  39  N.,  B.  28  W.—ln  sec.  13,  T.  39  N.,  R.  29  W.,  the 
Hanbury  formation  is  represented  by  exposures  of  black  slates  cut  by 
greenstones  (see  p.  471).  Between  this  place  and  the  center  of  sec.  19,  T. 
39  N.,  R.  28  W.,  there  are  no  exposures  except  here  and  there  a  small  knob 


ALGONKIAN,  HANBURY  SLATE.  485 

of  greenstone.  Within  the  last  few  years,  however,  the  formation  has  been 
opened  up  by  a  series  of  test  pits  and  shafts  extending  along  the  east-west 
quarter  line  of  the  last-named  section  for  a  distance  of  about  2,000  feet. 
(See  map,  fig.  54.) 

This  exploration,  which  was  made  under  the  direction  of  Mr.  Turner, 
of  Vulcan,  has  shown  the  presence  of  a  ferruginized  belt  inclosed  between 
normal  Hanbury  slates,  extending  in  an  east-west  direction  entirely  across 
the  explored  region.  Associated  with  the  slates  at  several  places  is  a 
greenstone  which  is  occasionally  fresh  and  dense,  but  which  usually  is 
much  decomposed.  On  the  north  side  of  the  ferruginized  belt  the  slates 
dip  north  at  high  angles.  On  the  south  side  they  ajDparently  dijj  high  to 
the  south.  On  both  sides  the  slates  are  light-gray,  much-sheared  clay 
slates,  cut  by  many  gaping  joint  cracks.  With  these  are  interbedded  a  few 
layers  of  quartzite  or  graywacke,   the  thickness  of  which  has  not  been 


Fig.  M. — Sketch  map  of  explorations  nt  Turner's  location,  near  center  of  see.  19,  T.  39  N.,  R.  28  W. 

determined.  Nearly  all  of  the  quartzite  is  sheared,  and  in  one  instance 
considerable  muscovite  or  other  light-colored  mica  has  been  developed. 
One  of  the  pits  on  the  south  side  of  the  ferruginized  belt  has  also  disclosed 
the  presence  of  a  well-defined  graphite  slate.  The  existence  of  this  mate- 
rial so  near  the  ferruginous  beds  recalls  the  presence  of  similar  material  in 
association  with  the  ore-beai-ing  beds  of  the  Curry  member  of  the  Vulcan 
formation,  and  suggests  the  interesting  possibility  that  it  may  signify  that 
the  same  processes  were  active  here,  which,  in  the  Vulcan  beds  gave  rise 
to  the  ore  deposits. 

The  ferruginous  band  averages  about  60  feet  in  width.  In  many  pits 
the  material  of  the  bands  looks  as  though  it  were  a  brecciated  chert  or  fine- 
grained quartzite,  cut  by  numerous  quartz  veins  and  by  thin  veinlets  of 
dense  hematite.  At  other  places  it  is  a  porous,  cherty,  ocherous  mass  con- 
taining crystalline  hematite,  forming  druses  on  the  walls  of  its  pores  and 


486  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

on  the  sides  of  joint  cracks.  In  the  deepest  shaft  the  ocherous  mass  seems 
to  be  a  superficial  layer  covering  a  bed  of  hard  hematite  ore.  This  ore 
appears  in  two  varieties.  In  one  it  is  a  dense  black  or  dark-red  hematite, 
interlaminated  with  thin  layers  of  yellowish-gray  chert,  or  a  dense,  banded 
ore,  made  iip  of  layers  diff"ering  slightly  in  texture.  The  second  variety  is 
porous  and  crystalline,  and  the  pores  are  studded  with  crystals  of  hematite. 
The  ore  that  has  been  seen  differs  in  character  from  that  of  the  great  ore 
deposits  in  the  Vulcan  formation,  but  is  similar  to  that  of  the  vein-like 
material  that  sometimes  occurs  in  the  jaspilites  as  narrow  bands,  which  are 
interpolated  parallel  to  the  bedding.  While  it  is  not  possible  to  see  the 
relations  of  the  ferruginous  belt  to  the  slates  on  both  sides,  it  seems  prob- 
able that  the  ferruginous  zone  is  along  a  line  of  crushing  and  fracture,  and 
that  the  hematite  was  deposited  within  it  in  the  same  manner  as  that  in 
which  the  ores  were  deposited  iu  the  brecciated  zones  within  the  Vulcan 
formation. 

POSSIBLE  IRON-ORE  DEPOSITS. 

From  YQYj  early  times  iu  the  exploration  of  the  Menominee  district 
there  has  been  much  speculation  as  to  the  possibility  of  discovering 
workable  ore  deposits  in  the  great  slate  area  between  the  Chicago  and 
Northwestern  Railway  and  the  southern  area  of  Quinnesec  schists.  The 
discovery  of  valuable  ore  beds  at  Commonwealth  and  Florence,  in  Wiscon- 
sin, in  slates  resembling  those  of  the  Hanbury  formation,  has  given  rise  to 
the  belief  that  similar  ores  will  sometime  be  found  in  the  slates  east  of  the 
Menominee  River.  That  so  few  explorations  have  been  made  in  this  area 
is  exjjlained  by  the  fact  that  few  clues  have  been  available  to  guide  the 
explorer  in  locating  drills  and  test  pits.  Exposures  are  scarce,  and  the 
mantle  of  drift  is  so  thick  that  explorations  can  not  be  intelligently  under- 
taken. Even  if  ore  bodies  exist,  they  would  be  very  difficult  to  find. 
Nevertheless,  as  has  been  indicated  above,  at  a  number  of  places  within 
the  slate  area  groups  of  test  pits  have  been  sunk,  and  from  these  lean  ores 
have  been  obtained.  In  some  cases  the  material  is  only  ferruginous  slate, 
and  in  other  instances  it  appears  to  be  red  ocher.  In  a  few  cases,  however, 
mixtures  of  chert  and  iron  oxide  have  been  found  that  resemble  some  of 
the  mixed  cherts  and  ores  from  the  Michigamme  slates  of  the  Marquette 
district,  and  in  several  cases  these  are  banded.  Thus  far,  however,  nothing 
has  been  discovered  that  would  lead  to  the  belief  that  large  ore  bodies 


ALGONKIAN,  HANBURY  SLATE.  487 

exist  at  any  of  these  places.  But  notwithstanding  the  unfavorable  results 
hitherto  reached  by  explorations,  the  conclusion  that  no  ore  bodies  exist  in 
the  slate  areas  should  not  be  assumed.  The  slates  have  been  pierced  at 
only  a  few  places,  and  at  these  places  there  has  xmquestionably  been 
deposited  some  ore  material.  That  ore  bodies  of  workable  size  have  not 
been  discovered  may  be  due  to  the  fact  that  the  explorations  were  not 
made  in  situations  that  presented  conditions  favorable  to  the  accumulation 
of  the  ores,  or  it  ma)^  be  due  to  the  absence  of  sufficient  ferruginous 
material  in  the  slates  at  these  places  to  furnish  large  quantities  of  iron  oxide. 

In  describing  the  lithological  features  of  the  Hanbury  slate  reference 
was  made  to  the  j^resence  of  iron  carbonates  in  the  calcareous  slates  and 
dolomites  in  the  lower  portion  of  the  formation  and  to  their  alteration 
products.  Under  favorable  conditions  these  carbonates  have  j^artially  or 
completely  changed  into  oxide.  Crusts  composed  largely  of  the  hydrated 
oxide,  limonite,  are  noticeable  on  all  their  exposed  surfaces,  and  grada- 
tions between  the  dolomites  and  ferruginous  cherts  are  observable  in  several 
places.  Under  favorable  conditions  of  environment  and  with  suitable 
basins  furnished  in  which  to  accumulate  the  ore  produced,  there  seems  to 
be  no  valid  reason  why  there  should  not  be  formed  in  the  Hanbury  slates 
of  the  Menominee  district  ore  deposits  of  equal  size  to  those  formed  in  the 
slates  of  the  Florence  and  Iron  River  districts.  It  is  probable,  however, 
that  the  ores  would  be  non-Bessemer,  and  therefore  quite  unlike  those  in 
the  Vulcan  fonnation. 

The  same  rules  to  be  followed  in  exploring  the  Vulcan  beds  for  ore 
deposits  should  also  be  followed  in  exploring  the  Hanbury  slates.  In  the 
latter  case,  however,  there  is  much  greater  difficulty  in  selecting  favorable 
sites  for  the  location  of  the  exj^lorations  than  in  the  case  of  explorations  in 
the  Vulcan  area.  In  the  latter  area  the  possible  positions  of  the  ore  deposits 
are  in  a  narrow  belt  limited  on  the  one  side  by  the  Randville  dolomite  and 
on  the  other  by  the  Hanbury  slate.  Moreover,  marginal  folds  in  the 
dolomite  are  comparatively  easily  detected. 

The  Hanbury  areas  on  the  other  hand  are  broad,  and  the  folding  of 
the  slates  is  of  an  exceedingly  complicated  character.  Before  locating 
exploring  plants  in  this  area  the  ground  should  be  closely  examined  with  a 
view  to  securing  the  most  favorable  environment  possible,  for  it  is  a  well- 
established  fact  that  it  is  only  in  exceptionably  favorable  situations  withia 


488  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

the  slate  area  that  ore  deposits  of  workable  size  have  been  developed,  and 
that  explorations  in  any  other  than  the  most  favorably  situated  locations 
will  result  in  a  waste  of  money  and  energy.  If  possible,  the  following 
conditions  should  be  met  by  the  sites  selected : 

First.  Since  the  ore  material  is  derived  from  iron  carbonates,  and  these 
are  known  to  exist  only  in  the  dolomites,  cherts,  and  calcareous  slates,  the 
explorations  should  be  confined  to  areas  near  those  known  to  be  under- 
lain by  these  rocks,  which,  when  exposed  to  the  weather,  may  be  identified 
by  the  coating  of  limonite  that  covers  their  weathered  surfaces. 

Second.  The  most  favorable  situations  for  ore  concentration  are  the 
troughs  of  pitching  synclines  with  impervious  bottoms.  Hence  search 
should  be  made  for  pitching  folds.  If  such  folds  can  be  found,  and  it  can 
be  further  determined  that  the  folding  involves  beds  of  argillaceous  slates 
or  other  impervious  rocks,  these  furnish  conditions  favorable  for  ore 
concentration. 

Third.  In  the  Crystal  Falls  district  carbonaceous  shales  are  often  asso- 
ciated with  the  ore  bodies,  and  in  the  Menominee  district  graphitic  slates 
are  often  associated  with  the  Curry  ores,  some  of  the  material  of  which  is 
almost  certainly  original.  Therefore,  if  situations  can  be  found  where  car- 
bonaceous slates  occur  in  pitching  synclines  below  rocks  containing  iron 
carbonate,  the  conditions  niay  be  regarded  as  exceptionally  favorable  for 
the  accumulation  of  ore  dej^osits. 

Fourth.  Percolating  waters  are  the  agents  of  the  process  of  concentra- 
tion ;  consequently  localities  at  which  the  rock  masses  have  been  shattered, 
thus  affording  easy  passage  to  the  water,  are  places  particularly  desirable 
for  testing. 

In  a  set  of  slates  as  closely  folded  as  are  the  Hanbury  there  may 
somewhere  be  found  places  where  the  conditions  outlined  are  fulfilled,  and 
in  such  places  ore  bodies  will  be  found,  if  they  exist  anywhere  in  the 
slate  area. 

Thus  it  appears  that,  although  no  ore  bodies  of  value  have  thus  far 
been  discovered  in  the  slates,  the  possibilities  of  the  formation  have  not  by 
any  means  been  exhausted.  A  more  extensive  exploration  of  the  slate 
formation  is,  perhaps,  warranted  before  the  field  is  finally  abandoned  as 
worthless,  v 


CHAPTER   VI. 

THE   PALEOZOIC    SYSTEM. 

Limited  areas  of  Paleozoic  sediments  in  approximately  lioi'izontal 
sheets  are  found  to  lie  on  the  eroded  edges  of  the  Hiironian  and  Archean 
rocks  within  the  Menominee  trough,  and  a  wide  expanse  of  the  same  sedi- 
ments is  known  to  cover  all  the  older  rocks  at  the  eastern  border  of  the 
trough  and  to  extend  uninterruptedly  eastward  to  Green  Bay. 

The  Paleozoic  rocks  may  be  divided  into  two  formations.  The  lower 
beds  are  mainly  red  sandstone,  which  is  known  in  the  region  as  the  Lake 
Superior  sandstone.  The  upper  beds  are  porous  arenaceous  limestones, 
identified  by  Rominger  as  corresponding  to  the  Chazy  and  Calciferous 
formations  of  the  Ordovician  in  the  Eastern  States.  This  formation  is 
designated  the  Hermansville  limestone  on  the  map  forming  PI.  IX.  The 
sandstones  and  possibly  the  limestones  at  one  time  must  have  spread  con- 
tinuously over  the  entire  Menominee  district,  as  they  now  do  over  the 
region  to  the  east.  West  of  Waucedah,  however,  they  have  been  generally 
eroded  from  the  valleys,  leaving  remnants  as  isolated  patches  on  the  tops 
of  the  higher  hills.  East  of  Norway  both  the  sandstones  and  the  limestones 
can  still  be  found  at  many  points,  but  west  of  this  place  the  limestone  has 
been  identified  at  only  one  locality.  The  apparent  absence  of  the  limestone 
from  the  western  portion  of  the  district  may,  however,  be  due  to  the  fact 
that  exposures  are  rare,  indeed  practically  unknown,  on  the  tops  of  the  hills 
where  the  limestone  would  naturally  occur. 

SECTIOIV   1.     LAKE    SUPERIOR   SANDSTOKE. 

CHARACTER    AND    RELATIONS. 

The  Lake  Superior  sandstone,  according  to  Rominger,  consists  of  a 
lower  portion,  partly  cemented  by  an  iron  oxide  and  consequently  red  in 
color,  and  an  upper  portion,  in  which  the  cement  is  partly  calcareous  and 
the  color  white.     Its  total  thickness  is  estimated  at  300  feet. 

489 


490  THE   MENOMIKEE  IRON-BEARING  DISTRICT. 

The  relations  of  the  sandstone  to  the  underlying  formations  are  always 
practically  the  same.  Whether  on  the  tops  of  hills  or  in  the  depressions 
between  the  hills  the  horizonal  beds  of  the  yomiger  rock  always  rest 
unconformably  upon  the  upturned  and  truncated  layers  of  the  older  series. 
In  the  mines  and  open  pits  visible  contacts  between  the  sandstone  and  the 
underlying  rocks  are  numerous,  and  in  every  case  the  contact  is  an  uncon- 
formable one.  Perhaps  the  best  of  these  is  at  the  west  end  of  the  Quinne- 
sec  pit  (see  PI.  XLIII),  where  the  shore-line  conditions  that  prevailed  at  the 
time  the  sandstone  was  deposited  are  very  clearly  exhibited.  Similar  con- 
tacts are  to  be  seen  at  several  places  within  the  Pewabic  and  the  Cuff  mines 
and  in  the  open  pits  of  the  Norway  and  the  Cyclops  mines. 

Moreover,  not  only  is  the  sandstone  separated  from  the  Huronian 
rocks  by  a  discordance  in  bedding,  but  its  basal  layers  always  contain  a 
great  deal  of  material  deri^■ed  from  the  immediately  subjacent  formations. 
Where  the  underlying  rocks  are  those  of  the  Randville  formation  the 
inclosed  fragments  consist  of  bowlders  of  cherty  quartzite  and  dolomite. 
Where  the  underlying  rocks  belong  to  the  Vulcan  formation  the  basal 
member  of  the  sandstone  is  an  ore  and  jasper  conglomerate,  composed  of 
huge,  rounded  bowlders  of  ore  and  large  sharp-edged  fragments  of  ferru- 
ginous quartzose  slate  and  jasper  in  a  matrix  consisting  of  quartzose  sand, 
numerous  small  pebbles  and  fragments  of  ore-formation  mateiials,  quartzite, 
and  occasional  pebbles  of  white  quartz,  of  granite  or  of  other  members 
of  the  Archean  system.  Some  of  these  conglomerates  are  exceedingly 
handsome. 

In  a  few  instances  the  proportion  of  ferruginous  material  is  so  great 
that  the  conglomerates  have  been  utilized  as  sources  of  iron  ore.  A  deposit 
of  this  kind  was  formerly  worked  by  the  operators  of  the  Quinnesec  mine, 
and  another  has  recently  been  worked  by  the  Pewabic  company.  The 
latter  was  reached  by  the  open  pit  in  the  southeast  quarter  of  sec.  32, 
T.  40  N.,  R.  30  W.,  known  as  the  Pewabic  pit.  Although  at  this  place  the 
rock  immediately  underl}'ing  is  dolomite,  the  amount  of  iron  ore  in  the 
conglomerate  is  so  greal  that  the  company  operating  the  pit  felt  warranted 
in  erecting  concentrating  works  on  the  property  for  the  separation  of  the 
ore  from  the  sandstone  (PL  XXII,  B).  In  the  summer  of  1898  the  yield 
of  ore  from  the  concentrator  Avas  5,000  tons. 


PLATE    XLIII. 


491 


PLATE   XLIII. 

VIEW  OF  UNCONFORMITY  BETWEEN  THE  TRADERS  JASPILITES  AND  THE  LAKE  SUPERIOR 

SANDSTONE. 

West  side  of  Quinnesec  open  pit.  The  rocks  to  the  left  are  even-banded  Traders  jaspilites 
dipping  north.  Above  these,  and  to  the  right,  is  the  Lake  Superior  sandstone.  Its  top  layers  are 
practically  horizontal,  but  near  the  contact  with  the  jaspilites  the  dip  is  steep  to  the  north,  conforming 
with  the  dip  of  the  surface  of  the  underlying  rock.  The  lower  layers  of  the  sandstone  series  consist 
of  coarse  conglomerates  containing  abundant  angular  fragments  of  the  jaspilites.  Interlaminated 
with  these  are  layers  of  fine  sand.  All  beds  thicken  with  increasing  distance  from  the  contact,  and 
their  included  fragments  become  less  angular.  Cross  bedding  can  be  detected  in  the  sandstone  layer 
beneath  the  heavy  bed  of  conglomerate. 

492 


PALEOZOIC,  LAKE  SUPERIOR  SANDSTONE.  493 

AGE  OF  LAKE  SUPERIOR  SANDSTONE. 

Although  Rominger  states  that  there  is  no  record  ot  any  recognizable 
fossils  from  the  sandstone,  nevertheless,  because  of  its  position  beneath 
the  limestones,  he  correlates  it  witli  the  Potsdam  of  New  York.  Since 
the  publication  of  Rominger's  report  several  pieces  of  fossil-bearing  sand- 
stone have  been  obtained,  which,  according  to  reliable  authority,  came 
from  the  ledge  through  which  the  Pewabic  mine  shafts  near  Iron  Mountain 
were  driven.  One  of  these  contains  numerous  fragments  of  trilobites,  some 
of  which  were  determined  by  Dr.  Walcott  as  "the  heads  of  small  trilobites, 
probably  BikeUocephalus  misa;"  others  are  "fragments  of  a  large  species  of 
BiMlocephalus."  According  to  Walcott,  "these  indicate  the  Upper  Cam- 
brian horizon  of  the  Mississippi  Valley  section."  Other  pieces  are  filled 
with  fragments  of  brachiopod  shells.  In  most  cases  these  are  ground  up 
into  veiy  small  portions,  but  occasionally  a  layer  is  found  in  which  whole 
valves,  and  indeed  entire  shells,  are  abundant.  In  every  case  seen  the 
shell-bearing  layers  are  interbedded  with  coarsely  conglomeratic  layers, 
indicating  that  they  must  have  been  formed  in  shallow  water  near  a  shore 
line.  Mr.  Schuchert,  of  the  United  States  National  Museum,  has  been  kind 
enough  to  examine  some  of  the  best  preserved  of  these  shells  and  has 
pronounced  them  to  be  Lingulepis  pinniformis. 

The  discovery  of  these  fossils  in  the  sandstone  at  Iron  Mountain  is 
particularly  interesting,  since  they  furnish  the  data  by  which  the  rock  is 
identified  as  a  portion  of  the  St.  Croix  series  of  the  Upper  Mississippi 
Valley,  which  in  turn  is  stratigraphically  equivalent  to  the  Potsdam 
sandstone  in  the  Adirondack  region.  Through  tlie  Menominee  rock  is  like- 
wise established  the  age  of  the  sandstone  bordering  the  south  side  of  Lake 
Superior,  since  the  Menominee  sandstone  is  traceable  directly  by  almost  con- 
tinuous exposures  into  the  sandstone  at  Ashland,  Marquette,  and  other  points 
on  the  south  shore  of  the  lake.  Therefore  this  sandstone  likewise  must  be 
the  equivalent  of  the  St.  Croix  sandstones.  This  view  has  been  consistently 
maintained  by  nearly  all  writers  on  the  geology  of  the  Lake  Superior 
region,  but  it  was  based  exclusively  on  stratigraphical  arguments,  since 
the  rock  had  nowhere  been  seen  to  contain  fossils  that  it  was  possible  to 
identify.     Walcott,  in  his  review  of  the  literature  of  the  Cambrian  series," 

o  Walcott,  C.  D.,  Correlation  papers— Cambrian:  Bull.  U.  S.  Geol.  Survey  No.  81,  1891,  p.  338. 


494  THE   MEXOMEsEE  IRON-BEARING  DISTRICT. 

concluded  that  the  Lake  Superior  sandstone  "occupies  the  exact  strati- 
graphic  position  of  the  fossiliferous  St.  Croix  or  'Potsdam'  sandstone  of 
Wiscon.sin."  He  continues:  "Although  not  considering  it  proved  that  the 
two  sandstones  are  exactly  contemporaneous,  I  think  that  for  all  practical 
geological  classification  they  may  be  considered  equivalent  deposits." 
The  discovery  of  a  poi-tion  of  the  St.  Croix  fauna  in  these  sandstones 
removes  the  doubt  as  to  their  contemporaneity  with  the  St.  Croix  beds 
and  enables  us  to  con-elate  the  two  sandstones  ^vithout  much  fear  of  error. 

SECTIOX   2.    HERSr.AXSVIliU:   UMESTOXE. 

The  general  character  of  the  Hennans\'ille  lunestone  "is  that  of  a 
coarse-grained  sandstone,  with  abundant  calcareous  cement,  in  alternation 
with  pui'e  dolomite,  or  sometimes  oolitic  beds."  The  limestone  may  be  seen 
near  the  top  of  Hughitt  Bluff,  east  of  Iron  Mountain,  on  the  north  side  of 
the  road  between  the  Pewabic  and  the  Walpole  mines,  and  also  on  the  bluff 
northeast  of  Norway  and  at  several  places  on  the  hills  north  of  Waucedah. 
Its  maximum  thickness,  according  to  Rominger,  is  about  100  feet,  but  this 
maximum  is  rarely  reached  in  the  Menominee  district.  Only  a  few  fossils 
have  been  reported  fi-om  it.  Rominger  states  that  it  has  yielded  a  few 
fragments  of  mollusean  shells.  To  these  may  now  be  added  a  broken 
Orthoceras,  a  fragment  resembling  a  piece  of  a  Cyrtoceras,  a  gasteropod, 
and  several  other  fragmeutai-y  forms  found  in  the  top  layer  on  the  bluff 
northeast  of  Norway. 

The  areas  within  which  the  limestone  is  known  to  occur-  are  so  small 
that  no  attempt  has  been  made  to  differentiate  them  from  the  Cambrian 
areas  on  the  general  map. 


CHAPTER    VII. 

OUTLINE  OF  GEOLOGICAL  HISTORY. 

RESU3I]6   OF   FORMATIOIVS. 

Before  giving  a  brief  oiitline  of  the  history  of  the  district  it  may  be 
well  to  recall  the  general  succession  of  formations  aiid  their  distribution. 
The  disti-ict  is  bordered  by  areas  of  Archean  schists  and  granites.  The 
Huronian  sediments  of  the  district  are  in  a  trough  between  these  older 
rocks.  Structurally  this  trough  is  a  synclinorium,  composed  of  several 
important  anticlines  and  synclines.  The  Lower  Menominee  series  com- 
prises 1,050  to  1,250  feet  of  quartzites  and  conglomerates  that  have  been 
called  the  Sturgeon  quartzite,  1,000  to  1,500  feet  of  dolomites,  with  subor- 
dinate amounts  of  calcareous  slate  and  chert,  designated  the  Randville 
doloiriite,  and  possibly  small  patches  of  the  iron-bearing  Negaunee  forma- 
tion. Tlie  Upper  Menominee  series  comprises  the  Vulcan  formation,  650 
feet  thick,  and  the  Hanbury  slate.  The  Vulcan  formation  includes  three 
members,  the  iron-bearing  Traders  member,  consisting  largely  of  detrital 
ores  and  jaspilites,  but  having  basal  layers  of  slate,  quartzite,  and  con- 
glomerate; the  Brier  membei-,  composed  of  ferruginous  and  siliceous  slates; 
and  the  Curry  member,  consisting  of  quartzites,  ferruginous  quartzose  slates, 
jaspilites,  and  ores.  The  Hanbury  slate  is  maiidy  argillaceous,  but  in 
places  is  calcareous,  and  includes  small  beds  of  dolomite  and  ferruginous 
chert. 

SUCCESSION^  OF  EVENTS. 

^4  rehean. — The  history  of  the  Archean  rocks  is  an  extraordinarily  com- 
plex one,  which  will  not  here  be  analyzed.  It  is  sufficient  to  say  that  the 
ancient  Quinnesec  schists,  wholly  of  igneous  and  largely  of  volcanic  origin, 
were  intruded  in  a  most  complex  fashion  by  various  igneous  rocks,  of  which 
granite  was  the  most  abundant.  This  complex  of  rocks  went  through  a 
long  series  of  epeirogenic  and  orogenic  movements,  with  attendant  meta- 
morphosis and  deep  denudation,  before  Algonkian  time. 

495 


496  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

Lower  Menominee  deposition. — By  transgressiou  of  the  sea,  due  to  sub- 
sidence of  the  land  or  rise  of  the  sea,  or  both,  the  Menominee  district  was 
finally  covered  hx  water,  and  Lower  Menominee  Algonkian  deposition 
began.  Originall}'  the  sediments  were  laid  down  as  a  set  of  approximately 
horizontal  beds  on  a  basement  composed  of  Archean  rocks  similar  to,  if 
not  identical  with,  the  material  constituting  the  rims  of  the  trough.  The 
first  deposit  of  the  advancing  sea  was  the  basal  conglomerate  of  the  Stur- 
geon quartzite.  Following  this  conglomerate  was  a  thick  layer  of  sand- 
stone, which  later  was  consolidated  into  quartzite.  The  deposition  of  a 
considerable  thickness  of  sand,  which  at  several  horizons  is  ripple  marked, 
shows  that  the  district  must  have  continued  to  subside  during  Sturgeon 
time.  Apparently  toward  the  end  of  the  Sturgeon  epoch  the  water  became 
too  deep  for  sandstone  formation,  and  the  nonclastic  sediments  of  the  Rand- 
ville  dolomite  were  deposited.  These  are  now  cherty  crystalline  dolomites 
and  marbles,  but  there  is  every  reason  to  believe  that  the  original  form 
of  the  material  was  an  ordinary  siliceous  magnesian  limestone.  The  time 
represented  by  the  Randville  dolomite  was  probably  long,  for  the  thickness 
of  limestones  deposited  was  1,000  feet  or  more.  Possibly,  as  a  result 
of  iipbuilding  with  shallowing  of  the  sea,  or  other  imknown  conditions, 
the  carbonates  being  deposited  changed  in  character  and  bore  a  large 
amount  of  iron.  At  this  time  the  cherty  iron-bearing  carbonates  and 
greenalite  nodules  were  produced.  Later  these  were  transformed  into  the 
feiTUginous  cherts  and  jaspilites  of  the  Negaunee  formation.  Whether  or 
not  later  formations  were  deposited  during  Lower  Menominee  time  upon 
the  Neo'aunee  formation  is  uncertain. 

The  formations  of  the  Lower  Menominee  series  were  certainly  depos- 
ited over  a  considerable  area  in  the  Menominee  district,  and  the  equiva- 
lents of  these  formations  were  deposited  north  of  the  Menominee  district  in 
the  Crystal  Falls  and  Marquette  districts.  Whether  or  not  the  Lower 
Menominee  formations  were  deposited  upon  the  Quinuesec  schists  is  uncer- 
tain. It  is  possible  that  the  Quinnesec  schists  were  land  areas  during  a 
large  part  of  Lower  Menominee  time  and  that  the  iron  for  the  Negaunee 
formation  was  derived  from  these  heavily  ferruginous  rocks  within  and 
bordering  the  district  mapped.  The  apparent  entire  absence  of  the  Lower 
Menominee  formations  about  the  western  area  of  Quinnesec  schist  is  difficult 
to  understand.     The  most  plausible  explanation  for  this  area,  and  possibly 


OUTLINE  OF  GEOLOGICAL  HISTORY.  497 

for  the  southern  area,  is  that  the  Lower  Menominee  formations  were  there 
deposited  and  were  subsequently  removed  by  erosion.  These  formations, 
resting-  upon  the  Quinnesec  schists,  might  have  been  composed  of  softer 
material  than  the  resistant  formations  adjacent  to  the  granite  area  on  the 
north  side  of  the  trough,  and  therefore  may  have  been  more  easily  erodible. 

In  any  case,  it  is  highly  probable  that  the  different  formations  were 
not  deposited  in  uniformly  thick  layers  throughout  the  district.  If  all  the 
formations,  or  the  lower  ones,  were  not  deposited  upon  the  Quinnesec 
schist,  each  higher  stratum  overlapped  the  one  next  below  it  in  j^assing 
toward  the  land  areas  of  Quinnesec  rocks. 

Inter-Menominee  unconformity. — Following  the  long-continued  deposi- 
tion of  Lower  Menominee  time  the  district  was  raised  above  the  sea. 
Apparently  this  uplift  was  accompanied  by  only  very  gentle  folding.  The 
reason  for  this  belief  lies  in  the  apparent  conformity  of  strike  and  dip  of  the 
Upper  and  Lower  Menominee  series.  However,  it  is  explained  in  another 
connection  that  such  an  erosion  interval,  with  no  great  discordance  in  strike 
and  dip,  may  mark  a  very  great  hiatus,  and  such  is  believed  to  have  been 
the  case  in  the  Menominee  district.  The  evidence  that  such  a  hiatus 
exists  between  the  lower  and  the  upper  iron-bearing  series  is  not  found  in 
the  Menominee  area,  but  in  other  areas  south  of  Lake  Superior.  In  the 
Marquette  district,  for  instance,  the  inter-Huronian  orogenic  movements 
and  denudation  were  of  a  most  profound  character.  As  soon  as  the 
Menoininee  area  rose  above  the  water,  erosion  began  and  continued  until 
all  the  Negaunee  formation  was  removed  through  the  central  and  northern 
parts  of  the  district,  and  probably  also  all  of  the  Lower  Menominee  forma- 
tions from  that  part  of  the  district  adjacent  to  the  areas  of  the  Quinnesec 
schists.  However,  as  has  already  been  said,  these  schist  areas  may  have 
been  above  water  during  much  of  Lower  Menominee  time,  in  which  case  it 
would  not  be  necessary  to  suppose  that  denudation  removed  from  them 
the  Lower  Menominee  formations. 

Upper  Menominee  deposition. — During  the  later  stages  of  the  inter- 
Menominee  denudation  the  sea  again  gradually  overrode  the  district. 
Evidently  at  this  time  the  area  was  uneven,  though  not  mountainous,  for 
the  first  formation  laid  down  b}^  the  Upper  Menominee  sea  does  not  extend 
over  tlie  entire  district.  These  first  deposits  constitute  the  iron-bearing 
Traders  member  of  the  Vulcan  formation.     The  material  of  which    this 

MON  XLVI — Ott 32 


498  THE   MENOMINEE  IRON-BEARING  DISTRICT. 

member  is  composed  was  largely  derived  from  the  iron-bearing  Negaunee 
formation,  although  material  was  furnished  by  other  formations,  and  a 
portion  consisted  of  iron  carbonate  and  greenalite.  Therefore  the  basal 
layers  are  composed  of  quartzites  and  conglomerates,  the  bowlders  and 
smaller  detritus  of  which  consist  largely  of  iron  oxide  and  jasper,  with 
some  quartzite  and  dolomite.  Since  these  bowlders  could  have  come  only 
from  a  land  mass,  it  is  certain  that  the  Lower  Menominee  beds  at  this  time 
had  already  been  consolidated  and  were  at  least  partly  above  the  sea. 
Following  the  deposition  of  the  basal,  somewhat  coarse,  clastic  member 
of  the  Vulcan  formation,  there  came  a  time  of  relative  quiescence,  during 
which  the  muds  that  afterwards  solidified  into  the  Brier  slate  were  laid 
down.  Following  the  deposition  of  the  Brier  slate  the  mingled  fragmental 
and  nonfragmental  sediments  of  the  Cvirry  member  were  deposited.  At 
the  end  of  the  time  of  the  deposition  of  the  Vulcan  formation — that  is, 
at  the  close  of  the  deposition  of  the  iron-bearing  Curry  member — the  sea 
had  not  as  yet  spread  over  all  of  the  district.  The  area  covered  has  not 
been  accurately  determined,  and  the  Vulcan  formation  may  have  a  wider 
distribution  than  that  shown  on  the  map,  but  it  is  certain  that  the  sea 
had  not  covered  the  entire  district  and  that  some  areas  were  still  land, 
especially  those  occupied  by  the  hard,  resistant  dolomite.  This  is  shown 
by  the  fact  that  the  Hanbury  slate,  the  next  deposit  of  the  advancing  sea, 
at  various  places  rests  directly  upon  the  Randville  dolomite,  there  being  no 
intermediate  belt  of  Vulcan  formation.  The  deposition  of  the  Hanbury  slate 
required  a  long  time,  during  which  the  physical  conditions  varied,  for  min- 
gled with  the  ordinary  slates  are  subordinate  amounts  of  calcareous  slate, 
dolomite,  and  chert,  marking  brief  stages  of  jDartial  or  complete  nonfrag- 
mental sedimentation. 

Folding  and  metamorphism. — Following  the  deposition  of  Upper  Menom- 
inee time  the  district  was  again  raised  above  the  sea  and  was  subjected  to 
very  great  orogenic  forces.  The  rhajor  compressing  force  was  nearly  north- 
south.  As  a  result  of  compression  in  this  direction  the  areal  extent  of  the 
mass  of  Menominee  sediments  was  shortened  considerably,  probably  as 
much  as  one-half  Consequent  on  this  folding  two  great  anticlinoria  were 
formed,  bordering  tlie  northern  and  southern  sides  of  the  area,  and  a  great 
central  synclinorium  constituting  the  Menominee  trough.  The  northern 
and  southern  anticlinoria  naturally  expose  the  oldest,  or  Archean,  rocks. 
The  intermediate  synclinorium    is  occupied  by  the  Huronian  sediments. 


OUTLINE  OF  GEOLOGICAL  HISTORY.  499 

This  central  syncliuorium  consists  of  three  synchues  and  two  anticlines. 
Superimposed  on  these  folds  of  the  first  order  is  a  set  of  folds  of  the  second 
order,  on  these  a  set  of  folds  of  the  third  order,  and  on  these  folds  of  higher 
orders  to  those  of  microscopical  dimensions.  The  major  folds  of  the  Menom- 
inee synclinorium  are  illustrated  by  the  anticlines  of  dolomite;  the  folds  of 
the  second  order  by  the  synclines  within  the  Vulcan  formation,  in  which 
such  mines  as  the  Walpole,  Pewabic,  and  Aragon  occur;  the  folds  of  the 
third  order  by  the  two  separate  ore  deposits  of  the  Walpole.  From  an 
economic  point  of  view,  therefore,  it  is  necessary  to  take  into  account  at 
least  the  three  major  orders  of  folds. 

In  addition  to  the  intense  north-south  compression  there  was  very 
strong  compression  in  an  approximately  east-west  direction,  or,  to  speak 
more  exactly,  parallel  to  the  direction  of  tlie  trough.  This  compression 
produced  folds  at  right  angles  to  the  longitudinal  folds,  so  that  the  east- 
west  folds  of  the  various  orders  have  a  pitch.  In  some  cases  this  pitch 
is  comparatively  slight,  but  in  other  cases  it  is  very  steep,  as  high  as  40°, 
50°,  60°,  or  even  70°  or  more.  It  is  therefore  clear  that  the  east-west 
compression  was  of  great  importance.  While  the  north-south  compression 
produced  the  subordinate  synclines  holding  the  ore  bodies,  the  east-west 
compression  gives  these  folds  a  pitch,  and  thus  supplies  the  chief  final 
condition  for  the  production  of  the  ore  deposits. 

During  the  uplifting  and  folding  of  the  rocks  of  the  Menominee  series 
the  harder  formations  were  fractured  in  a  most  complicated  fashion,  and  all 
were  profoundly  metamorphosed.  The  sandstones  were  transformed  to 
quartzites,  the  limestones  to  crystalline  dolomite  or  marble,  the  iron-bearing 
formation  to  ferruginous  slates,  jaspilites,  and  ores,  the  muds  to  slates. 

Post-Huronian  unconformity. — Contemporary  with  the  uplifting  and 
folding  of  the  district,  which  must  have  produced  mountain  masses,  denu- 
dation was  steadily  going  on.  It  was  during  this  complex  series  of  trans- 
formations that  iron  oxide  was  concentrated  in  the  pitching  troughs  and  the 
ore  deposits  were  produced.  The  period  of  post-Huronian  folding  and 
erosion  occupied  the  great  length  of  time  represented  in  other  parts  of  the 
Lake  Superior  region  by  the  unconformity  between  the  Upper  Huroniau 
and  the  Keweenawan,  the  formation  of  the  entire  Keweenawan  series,  and 
the  great  unconformity  between  the  Keweenawan  and  the  Cambrian. 

Paleozoic  deposition. — During  the  later  stages  of  this  great  period  of 
denudation  the   Cambrian   transgression   was   slowly  making  its   way  in 


500  THE  MENOMINEE  IRON-BEARING  DISTRICT. 

North  Amenca  from  the  sovitheast  toward  the  northwest.  Finally  the 
'Cambrian  sea  reached  the  Menominee  district,  but  not  until  Upper  Cam- 
brian time.  At  this  time  the  topography  of  the  Menominee  area  was 
rough,  even  bluft'y.  The  Cambrian  deposits  filled  the  depressions  in  the 
preexisting  rocks  and  capped  even  the  highest  hills  of  the  district.  Where 
the  sandstone  lies  adjacent  to  or  upon  the  Vulcan  formation  the  basal 
member  of  the  Cambrian  contains  quantities  of  iron-ore  pebbles,  and  where 
the  topography  furnished  depressions  for  concentration  of  the  heavy 
material  these  beds  are  so  strongly  ferruginous  as  to  furnish  detrital  iron 
ores.  Sandstone  deposition  continued  to  the  end  of  the  Cambrian  ^Jeriod, 
at  which  time  the  water  had  become  sufficiently  deep  for  limestones  to  be 
deposited,  and  at  this  stage  of  the  history  the  Hermansville  limestone  was 
laid  down.  "Whether  Paleozoic  rocks  later  than  the  Hermansville  limestone 
were  deposited  in  the  Lake  Superior  region  is  uncertain. 

Post-Paleozoic  history. — Following  the  Paleozoic  period  of  deposition 
the  area  was  again  elevated  above  the  sea,  and  then  another  long  period  of 
denudation  began.  So  far  as  known,  this  erosion  period  continued  until 
late  in  Cretaceous  time.  Possibly  later  Cretaceous  sediments  were  laid 
down  over  the  Menominee  areas;  but  in  any  case,  following  Cretaceous 
time  the  region  was  again  elevated,  and,  so  far  as  we  know,  denudation 
has  since  continued.  Nearly  all  of  the  Silurian  limestone  has  now  been 
removed  from  the  district,  and  only  a  subordinate  amount  of  the  Cam- 
brian sandstone  remains  capping  the  higher  hills  and  filling  the  depres- 
sions in  some  of  the  subordinate  valleys.  During  this  period  of  erosion 
the  present  topography  of  the  district  was  largely  produced.  The  exact 
extent  to  which  this  topography  follows  the  pre-Cambi'ian  topography  can 
not  be  accurately  determined,  but  apparently  the  pre-Cambrian  topography 
has  had  an  important  influence  upon  present  topography.  As  the  result  of 
the  removal  of  the  greater  part  of  the  Paleozoic  rocks,  the  Huronian  and 
Archean  rocks  were  again  brought  to  the  sm-face. 

The  final  important  episodes  in  the  history  of  the  Menominee  district 
were  the  successive  advances  of  the  North  American  ice  sheet,  which 
modified  the  topography  of  the  district  by  erosion  and  by  deposition.  The 
glacial  deposits  constitute  a  mantle  which  subsequent  river  erosion  has  only 
partially  succeeded  in  removing,  and  which  has  prevented  fully  satisfactory 
determination  of  the  distribution  of  the  Vulcan  and  other  formations. 


CORRELATION  WITH  OTHER  DISTRICTS.  501 

CORRELATION  WITH  OTHER  IROK-BEARHSTG  DISTRICTS  OF  THE  LAKE 

SUPERIOR  REGION". 

The  attempt  to  correlate  the  various  formations  of  the  two  Huronian 
series  in  the  four  different  iron-bearing  districts  south  of  Lake  Superior 
shows  very  significantly  that  the  geological  history  of  pre-Cambrian  time 
was  extraordinarily  complex.  From  Archean  to  Upper  Cambrian  time,  in 
the  Marquette,  Crystal  Falls,  and  Menominee  districts,  the  areas  three  times 
emerged  from  the  sea  and  were  three  times  overridden  by  the  sea.  In  the 
Penokee  district  there  was  a  fourth  emergence  and  transgression  of  the 
sea.  The  epeirogenic  or  land-making  movements  were  accompanied  by 
orogenic  movements,  or  mountain  growths  of  varying  power,  but  some  of 
them  exceedingly  intense.  In  Huronian  time,  in  all  the  districts  except  the 
Menominee,  there  were  important  and  long-continued  periods  of  volcanism. 
The  erosive  forces  at  periods  when  the  districts  were  land  areas  found  rocks 
of  very  different  characters.  Here  they  were  resistant,  there  easily  denuded. 
As  a  consequence,  when  the  sea  encroached  at  the  close  of  Archean,  Lower 
Huronian,  and  Upper  Huronian  times,  the  country  in  detail  was  very  irreg- 
ular— was  in  fact  Iduffy,  but  not  mountainous.  Therefore  certain  areas 
were  covered  by  the  sea,  while  other  immediately  adjacent  areas  were  above 
the  water  and  were  being  actively  eroded.  As  a  consequence  of  all  these 
complex  conditions  we  have  unconformity,  overlap,  changes  in  the  charac- 
ters of  contemporaneous  sediments  along  the  strike  and  across  the  strike, 
disturbances  in  the  successions  due  to  volcanism,  close  folding,  and  attendant 
metamorphism,  and  all  of  these  phenomena  in  a  region  which  is  largely 
covered  by  glacial  drift. 

A  more  precise  correlation  of  the  Menominee  formations  with  those  of 
the  other  iron-bearing  districts  south  of  Lake  Superior  as  well  as  with  those 
to  the  north  of  the  lake  is  left  for  discussion  in  another  monograph  which 
will  treat  of  the  geology  of  the  entire  Lake  Superior  Basin. 


INDEX 


A. 

Page. 
Ac-id  intrusives  of  Northern  Complex,  lithology  of.  172-173 
Acid  intrusives  and  derived  schists,  lithology  of. .  149-154 
Adams,  F.  D.,  and  Nieolson,  J.  T.,  cited  on  cata- 

clastic  structure  in  limestone 213 

Algonkian  history  of  Menominee  district 496-498 

Algonkian  system,  general  character  and  definition 

of - .- -      1^6 

rocks  of ,  description  of - 20-31,176.488 

unconformity  in - 175-176 

Allen,  E.  T.,  analysis  by. 298,328 

Alteration  of  Brier  slate 327 

Alteration  products  in  gabbro.. —      139 

Amphibolites,  lithology  of 146-148 

Analysis,  Brier  slate.. 330 

chlorite-schist  from  Sturgeon  Palls 138 

dolomite  of  Chapin  mine 215 

of  Hanbury  formation 480 

efflorescence  on  ores 391 

gabbrofrom  Sturgeon  Falls 138 

gabbro,  schistose,  from  Sturgeon  FaUs 138 

granite-poi-phyry  from  Horserace  Rapids 153 

gi'anitite  from  Horserace  Rapids 153 

greenstone  from  Little  Quinnesec  Falls 143 

limestone  from  Sturgeon  River 60 

ore  of  Chapin,  Quinnesec,  and  Cornell  mines ...      383 

of  Curry  mine 348 

of  Menominee  district 382 

of  Traders  mine 311 

orthoclase     porphyroid    from    Big    Quinnesec 

FaUs 55 

orthoclase-paragonite-schist    from    Big    Quin- 
nesec Falls. 55 

paragonite-schist  from  Big  Quinnesec  Falls 55 

quartz-porphyry  from  Big  Quinnesec  FaUs 154 

schist  from  Little  Quinnesec  Falls 146 

serpentine  from  Chapin  ore 390 

slate  of  Traders  member 298 

talc  from  Chapin  ore 390 

taloose  schist  from  Aragon  mine 222 

Antoine,  Lake,  dolomite  ridge  south  of,  view  of 162 

Randville  dolomite  near 256,261-263 

section  through 59 

Aplite  of  Northern  Complex,  Uthology  of 172 

Appleton  and  Loretto  areas,  geological  map  of 404 

Aragon  fold,  description  of 242-245 

Aragon  and  Norway  folds,  geological  map  of 428 

sections  through 430 

Aragon  mine,  brecciation  near , 215 

ore  deposits  at  and  near. 4.33-435 

Randville  dolomite  east  of,  view  of 218 

section,  horizontal,  of,  at  eighth  level 433 

at  fifth  level. 243 

at  first  level 432 

at  sixth  level 244 


Page. 

Aragon  mine,  section,  longitudinal,  of 434 

section,  vertical,  through  Norway  mine  and 242 

structure  at 428 

talcose  schist  from,  analysis  of 222 

Vulcau  formation  at,  thickness  of 359 

Aragon  shaft  No.  1,  rocks  exposed  near 267 

Archean  complex,  map  of  exposures  near  contact 

of  Sturgeon  quartzite  and 186 

Archean  history  of  Menominee  district 495 

Archean  rocks,  features  of 30,103 

Archean  system,  discussion  of 1.30-174 

Argillaceous  rocks  in  Randville  dolomite 225-226 

Arkoses  and  graywackes  in  Sturgeon  quartzite..  181-183 

Augen-gneiss, lithology  of... 1.53 

Azoic  rocks,  origin,  abstract  of  paper  on 49 


Banding  of  Brier  slates 324 

of  Curry  member 340 

of  jaspilites  of  Curry  member 335-336 

Basic  intrusives.    See  Intrusives,  basic. 

Basic  lavas.    See  Lavas,  basic. 

Basic  schists.    See  Schists,  basic. 

Basic  tuffs.    See  Tuffs,  basic. 

Bayley,  W.  S.,  and  Van  Hise,  C.  R.,  cited  on  altera- 
tion of  carbonate 83 

cited  on  cherts  of  Marquette  district 230 

cited  on  concenti-ation  in  Marquette  district 396 

cited  on  literature  on  pro-Cambrian  of  Lake  Su- 

perior  region 99 

cited  on  Marquette  district 115 

cited  on  Negaunee  formation  in  Marquette  dis- 
trict   230,277 

cited  on  petrography  of  Archean  complex 40 

cited  on  pre-Cambrian  formations 43 

cited  on  slates  of  Kona  dolomite 266 

cited  on  structure  at  Chapin  mine 433 

report  on  Marquette  district,  abstract  of 112-113 

report  on  Menominee  district,  abstract  of 131-124 

Big  Quinnesec  Falls,  rocks  exposed  at 96, 157-158 

Birkinbine,  John,  cited  on  iron  ores  east  of  the 

Mississippi 85 

cited  on  production  of  iron  ores 103, 114 

Black  Creek,  sketch  map  of  exposures  along 194 

Sturgeon  quartzite  on 194-195 

Breen  mine,  geological  map  of  Enimett  mine  and  . .      452 
ore  deposits  at  Emmett  mine  and 45.3.455 

Brewster,  E.  E.,  analyses  by 215,298,330,383,390,891 

reference  to 388 

Breccia,  ore,  view  of,  near  contact  of  Traders  mem- 
ber with  Brier  slates,  Curry  mine 368 

Breccias  and  conglomerates,  dolomite,  occurrence 

and  character  of 215-221 

Breccia  ted  Rand  ville  dolomite,  plate  showing 218 

503 


504 


INDEX. 


Page. 

Breccia tion  of  cherts _ 228-229 

of  Vulcan  formation 362 

Brier  Hill,  dolomite  and  iron  formation  at__ 252 

Vulcan  formation  at,  thickness  of -. 359 

Brier  HiU  mine,  geological  map  of  vicinity  of 434 

ore  deposits  at -  -  434-437 

section  across  Vulcan  formation  near 435 

Brier  slate,  analyses  of 330 

distribution  of 320-323 

folds  in - 358 

in  Norway  pit,  view  of --- -      3<>4 

Uthologyof — -- 32'4-3:a 

occurrence  and  character  of - 26 

ore  breccia  near  contact  of  Traders  member, 

view  of -- 368 

origin  of  name  of -. - 40,291 

relation  of  Curry  member  to --- 350-351 

of  Traders  member  to 349-350 

thickness  of :360,361 

See  also  Vulcan  formation. 
Brooks,  T.  B.,  cited  on  rocks  at  the  Falls  of  theStm*- 

geon -.- 19* 

classified  list  of  rocks  observed  in  the  Huronian 
series  south  of  Lake  Superior,  abstract 

of .- 61 

geological  map  of  Menominee  iron  region  by. . ,        60 

reference  to 41 , 1 39 

report  on  geology  of  Menominee  Iron  region, 

abstract  of 63-68 

report  on  iron-bearing  rocks,  abstract  of 56-59 

report  on  Laurentian  rocks  of  Michigan,  ab- 
stract of... 68-69 

report  on  youngest  Huronian  rocks  south  of 
Lake  Superior  and  the  age  of  the  copper- 
bearing  series,  abstract  of 61 

work  of.. 36 

Brooks,  T.  B.,  and  Julien,  A.  A.,  catalogue  of  rocks 

by.  reference  to 60 

Brooks,  T.  B.,  and  Wright,  C.  E.,  geological  map  of 

Menominee  iron  region  by 66 

Brown,  E.  F.,  cited  on  distribution  of  phosphorusat 

Pewabic  mine 400,420 

Browne,  D.  H.,  cited  on  phosphorus  at  Ludington 

mine 400 

report  on  distribxition  of  phosphorus  in  Luding- 
ton mine,  abstract  of 89-92 

Burnt  shaft.  West  Vulcan  mine,  vertical   section 

through.... 443 

o. 

Calcareous  slates  and  dolomite  of  Hanbury  forma- 
tion  466-467 

Calcite,  crystals  of,  figures  showing 387 

occurrence  of 387-388 

Calumet  tongue,  course  and  width  of 34 

Carbonate,  iron.    See  Iron  carbonate. 

Central  Vulcan  area,  geological  map  of  portion  of 

West  Vulcanarea  and 438 

ore  deposits  of 449 

Chalcopyrite,  occurrence  of 388 

Chapin  mine,  dolomite  from,  analysis  of 215 

folding  at  and  near 338,248 

ore  of 86-87 

analyses  of 382,383 

ore  bodies  on  fifth,  sixth,  seventh,  and  tenth 

levels,  plate  showing 420 


Page. 

Chapin  mine,  ore  deposits  of 420-423 

section  at 105-106 

section,  vertical  of,  through  D  shaft 421 

through  No.  2and  C^  shafts 423 

slate  from,  analysis  of. 298 

topography  near 403 

views  east  from  D  and  A  shafts ._ 416 

Chapin  ore,  talc  and  serpentine  from,  analyses  of..      390 

Chapin-Pewabic  deposits,  description  of 414 

Chapin-Pe wabic  folds,  geological  map  of 423 

Chert,  brecciation  of 228-229 

fold  in,  at  Iron  Hill,  view  of 256 

in  Hanbury  slate 476-486 

Cherts  and  ferruginous  oxides  of  Hanbury  forma- 
tion  466-467 

Cherty  quartz  rocks,  comparison  of,  with  rocks  of 

Marquette  and  Gogebic  districts 239-230 

in  Randville  dolomite 226-233 

origin  of 230-232 

Chippewa  Island,  slates  at 44 

Chlorite-schist,  analysis  of,  from  Sturgeon  Palls...      138 

lithology  of 145-146 

of  diorite  of  Little  Quinnesec  Palls,  description 

of 140 

occurrence  of. 158,163 

Clay  slates  of  Hanbury  formation 46^-464 

Clements,  J.  M.,  assistance  by __ 33 

cited  on  volcanics  of  Crystal  Falls  district 165 

Clements,  J.  M.,  and  Smyth,  H.  L.,  cited  on  Crystal 

Falls  district.. 34 

cited  on  geology  of  Felch  Mountain  range. 56 

cited  on  Sturgeon  quartzite  and  Randville  dol- 
omite  39 

cited  on  Sturgeon  quartzite  of  Felch  Mountain 

district 177 

report  on  Crystal  Falls  district,  abstract  of . ..  116-121 
Clifford  pit,  folds  in  Traders  jaspilite  in,  view  of . . .      256 

iron  content  of  rock  from  near 311 

jasper  bands  on  west  side  of,  contortions  in,  fig- 
ure showing 303 

j'aspilite  at,  sketch  showing  puckering  of 358 

ore  from,  analysis  of 383 

ore  deposit  at 408 

Concentrating  works  at  Pewabic  pit,  view  of. 368 

Conglomerates  in  Sturgeon  quartzites 179-181 

Conglomerate,  dolomite,  plate  showing 218 

Conglomerates  and  breccias,  dolomite,  occurrence 

and  character  of 215-321 

Conglomerate  and  quartzite  in  Traders  member.  300-307 

Contortions  in  jasper  bauds,  figure  showing. 303 

Cornell  mine,  ore  from,  analysis  of. 383 

ore  deposits  at 410 

shipments  from. _. 407 

Traders  member  at 293 

geological  map  of  Traders  mine  and 406 

Credner,  H  ,  cited  on  pre-Cambrian  formations 79 

cited  on  rocks  at  the  falls  of  the  Sturgeon 197 

report  on  porphyroid  schists,  abstract  of 55-66 

report  on  pre-Silurian  rocks,  abstract  of... 49-50 

report  on  pre-Silurian  structure  of  Upper  Pen- 
insula of  Michigan,  abstract  of. 51-55 

Cross  folding  in  Randville  dolomite 233-335 

Crystal  Falls  district,  shipments  from 35 

succession  in _ 122 

Cuff  mine,  dolomite  at,  dip  of 233,236 

geological  map  of  country  adjacent  to  Indiana 

mine  and 410 


INDEX. 


505 


Page. 

Cuff  mine,  jasper  from --- 308 

ore  deposits  at --- 41CM11 

pre-Camhrian  topograpiiy  at 129 

Eandville  dolomite  near __ -- 256 

shipments  from --- 407 

sketch  plan  of -.1 236 

Traders  member  at - - 292 

Vulcan  formation  near. _. -- -      286 

Cundy  mine,  ore  deposits  at - 427-428 

Curry  member  of  Vulcan  formation,  banding  of . . .      340 

distribution  of 331-333 

formation  of 355 

jasper  of - - 333-335 

jasper  band  in  jaspilite  of,  photomicrograph  of.      316 

lithologyot - —  333-349 

occurrence  and  character  of 26 

ore  of- - — 335 

photomicrograph  of  -  - 316 

origin  of  name - - -  40,291 

relation  of  Bi*ier  slates  to 350-351 

thickness  of - --  360,361 

See  also  Vulcan  formation. 

Curry  mine,  Curry  member  near. _. 339 

geological  map  of  vicinity  of 434 

ore  at -- 87 

ore  breccia  near,  plate  showing -. 368 

ore  deposits  at -- -- 487-439 

planof  No.  Spitof.- - - 438 

rocks  north  of --. - "2 

Curry  shaft  No.  1,  Brier  slate  at,  sketch  showing 

puckering  of  .-. — 358 

Curry  shaft  No.  2,  Vulcan  formation  at,  thickness  of      359 

Cyclops  mine,  contact  at. 72 

ore  at. 88 

ore  deposits  at  Norway  mine  and 428-431 

Cyrtoceras,  occurrence  of.. 494 

D. 

Diabase,  character  of 139 

in  Sturgeon  quartzite 185 

occurrence  of 156,157 

Dikellocephalus  misa,  occurrence  of 493 

Dikes  in  Northern  Complex 173 

Dikes  and  veins  in  Sturgeon  quartzite 185-186 

Diorite  along  Menominee  River 76 

occurrence  of 158 

Diorites  and  derived  schists,  description  of 139-141 

Dolomite,  analysis  of,  from  Chapin  mine 215 

analysis  of,  from  Hanbury  formation 480 

occurrence  of 386-387 

origin  of.. 2.30-232 

See  also  Bandville  dolomite. 
Dolomite  and  calcareous  slates  of  Hanbiiry  forma- 
tion.  466^67 

Dolomite  and  dolomitic  sandstone,  occurrence  and 

character  of 210-215 

Dolomite  belt,  Vulcan  formation  along 285 

Dolomite  bluffs  between  Quinnesec  and  Norway, 

view  of 208 

Dolomite  breccias  and  conglomerates,  occurrence 

and  character  of 215-221 

Dolomite  conglomerate  at  Iron  Hill,  view  of 218 

Dolomite  ridge  south  of  Lake  Antoine,  view  of 163 

Drainage,  features  of 20,126-127 

■R. 
East  Vulcan  area,  geological  map  of  Verona  area  and .      450 
East  Vulcan  mine,  oreat 87 


Page. 

East  Vulcan  mine,  ore  deposits  at 4.50-453 

section,  horizontal,  of,  at  eighth  level 4.50 

section,  vertical,  of,  through  shaft  No.  3 451 

through  shaft  No.  4 4.52 

Efflorescence  on  ores,  discussion  of 390-391 

Emmett  mine,  geological  map  of  Breen  mine  and  ..      452 

ore  at,  character  of 84 

ore  deposits  at  Breen  mine  and 453-455 

Eskil,  J.  J.,  photograph  by 416 

Palls  and  rapids  in  Menominee  Elver 132-133 

Felch  Mountain  district,  map  of  region  between  Me- 
nominee River  and 34 

Felsites,  schistose,  lithology  of.. 154 

Ferruginous  oxides  and  cherts  of  Hanbury  forma- 
tion.  _ 466-467 

Folding  in  chert  at  Iron  Hill,  view  of 256 

in  Hanbury  slate 30,469^70 

in  jaspilites  of  Vulcan  formation,  view  of 356 

in  Rand ville  dolomite 33,232-248,269-270 

in  Sturgeon  quartzite 21,186-187 

in  Traders'  jaspilite,  view  of -      356 

in  Upper  Menominee  series 284 

in  Vulcan  formation .356,359 

Folds.    See  also  Aragon  and  Norway  folds;  Chapin- 
Pewabic  folds. 

Forest  mine,  ore  deposits  at. 412-413 

Vulcan  formation  near 286 

Formations,  classiiication  of .38-39 

names  of 39-40 

Foster,  J.  W.,  catalogue  of  rocks  by,  reference  to..        49 

reference  to... 41 

report  by,  reference  to... 43 

report  on  Chippewa  land  district,  abstract  of  . .  43.45 

Poster,  J.  W.,  and  Whitney,  J.  D.,  report  on  age  of 

Lake  Superior  sandstone,  abstract  of  . . .        45 
report  on  Lake  Superior  land  district,  abstract 

of 45-48 

Pourfoot  Falls,  greenstones  at 97 

rocks  exposed  at 161,162,166-167 

Fulton,  John,  cited  on  methods  of  mining  in  the 

Menominee  range 89 

report  on  deposition  of  iron  ores  of  Menominee 

iron  range,  abstract  of 87-88 

Fnmee,  Lake,  limestone  near 73-78 

section  through  west  end  of 69 


Gresley,  W.  S.,  cited  on  organic  markings  in  Lake 

Superior  iron  ores 114 

photographs  by 118,120 

report  on  organic  remain  from  Huronian  series 

at  Iron  Mountain,  abstract  of 115-116 

Gabbro,  analysis  of,  from  Sturgeon  Falls 138 

in  Sturgeon  quartzite 186 

occurrence  of 157 

Gabbro,  schistose,  analysis  of,  from  Sturgeon  Falls .      1.38 
Gabbros  and  derived  schists,  lithological  descrip- 
tion of 136-139 

Gneisses,  banded,  lithology  of 170-171 

Goetz,  G.  W.,  cited  on  analyses  of  Lake  Superior 

ores 99 

Gogebic  range,  shipments  from 36 

Gold  in  Sturgeon  quartzite 185 

Granite  at  Falls  of  the  Sturgeon  Biver 75 

of  Northern  Complex,  occurrence  of 172 


506 


INDEX. 


Page. 

Granites,  gneissoid,  lithology  of 150-153, 169-170 

Granite-gneisses  and  gneissoid  granites,  lithology 

of 150-1.53 

Granite-poi-phry,  analysis  of,  from  Horserace  Rap- 
ids  153 

at  Horserace  Rapids _. -.-  161-152 

Granitite,  analysis  of, from  Horserace  Rapids 153 

Graywacke,  definition  of 180 

Graywackes  and  arkoses  of  Sturgeon  quartzite  . .  181-182 
Gray wackes  and  quartzites  of  Hanbury  formation  464-466 
Greenstone,  analysis  of,from  Little  Quinnesec  Falls.      143 

occurrence  of 166-167 

Greenstones,  coarse-grained,  in  western  Quinnesec 

area _ 163 

Greenstone-schists,  coarse-grained  varieties  of,  de- 
scription of 136-141 

fine-grained  varieties  of ,  description  of -,.  141-145 

lithology  of 162-163 

occurrence  and  age  of 92-93 

petrography  of 94r-98 

rocks  included  in 135 

Hanbury  Hill,  Hanbury  slate  at 472-475 

Hanbury  Lake,  rocks  west  of 73 

Hanbury  slate,  cherts  in 476-486 

distribution  of 462 

distribution  of  Vulcan  formation  and,  explana- 
tion of 370-;372 

dolomite  in,  analysis  of 480 

exposures  of 471-486 

folding  of 30,469-470 

igneous  rocks  intruded  in __ 468 

lithology  of 462-468 

occurrence  and  features  of 30 

ore  deposits,  possible,  in 486-488 

origin  of  name 40 

relation  of  Paleozoic  beds  to 471 

of  Randville  dolomite  to 366-370 

of  Vulcan  formation  to 365-366 

thickness  of 470 

topography  of 462 

Hardenburgh,  L.  M.,  acknowledgments  to. 34 

Helberg,  G.,  acknowledgments  to 34 

Hematite  in  conglomerate  of  Traders  member 306 

Hermansville  limestone,  character  of 31, 494 

Hill, .  reference  to 44 

Hills,  rocks  forming 126 

Hillyer,  V.  S.,  acknowledgments  to 34 

Hornblende-schists,  lithology  of 171-172 

in  southern  area  of  Quinnesec  schists 147 

Hoi-serace  Rapids,  character  of .-.      132 

granite-porphyry  at 151-152 

high  water  in,  view  of ^ 158 

log  jam  in,  view  of 158 

rocks  exposed  at 96,158-159 

Hubbard,  L.  Ij.,  cited  on  macroscopic  minerals  of 

Michigan 102 

Hughitt  Bluff ,  altitude  of 155 

jaspilites  at 301 

pre- Cambrian  topography  at  _ 129 

Hulst,  N.  P.,repoi     on  Menominee  Range,  abstract 

of 104^106 

Huronian  series,  character  of 64-65 

composition  of 50 

quartzites  of 82 

rocks  comprising 70 


Page. 
Huronian  series,  thickness  of 65 

Huronian  trough,  location  and  surface  features  of.      125 

I. 

Igneous  rocks  intruded  in  Hanbury  slate 468 

Indiana  mine,  dolomite  at,  dip  of 233,236 

geological  map  of  country  adjacent  to  Cuff  mine 

and 410 

iron  formation  and  dolomite  at 353 

ore  deposits  at 411-413 

Randville  dolomite  at,  width  of... 303 

shipments  from 407 

Ti*aders  member  near 293 

Vulcan  formation  near 286 

Intrusives  of  Northern  Complex,  lithology  of 172-174 

Intrusives,acid,  and  derived  schists,  lithology  of.  149-154 

Intrusives,  basic,  lithology  of. 173 

Iron  carbonate,  alteration  of... 83 

Iron  Hill,  brecciation  near 215 

chert  at,  view  of  fold  in : 256 

chert  near ._ 481-483 

conglomerate  at 219-220 

dolomite  conglomerate  at 218 

exposures  at,  map  of 480 

folding  at 234,236 

Hanbury  slate  and  Randville  dolomite  at,  rela- 
tion of 369 

Randville  dolomite  near 256-260 

width  of 203 

sandstone  mesa  at 128 

Vulcan  formation  near 386 

Iron  ores, organic  markings  in,  plates  showing...  118,120 

report  on,  abstract  of 78 

-S'ee  aho  Ore  deposits. 
Irving,  R.  D.,  cited  on  classification  of  early  Cam- 
brian and  pre-Cambrian  formations 85 

cited  on  Huronian  group 85 

cited  on  origin  of  ferruginous  schists  and  iron 

ores  of  Lake  Superior  region 83 

cited  on  rocks  at  the  Falls  of  the  Sturgeon 198 

geological  map  of  Menominee  iron  region  by  ...        94 
report  on  Archean  formations  of  the  Northwest- 

ei-n  States,  abstract  of.. 81-82 

report  on  copper-beai-ing  rocks  of  Lake  Superior, 

abstract  of 79 

report  on  greenstone-schists,  abstract  of 92-94 

report  on  iron  ores,  abstract  of 78 

reference  to 41 

work  of 36 

Irving,  R.  D.,  and  Van  Hise,  C.  R.,  cited  on  concre- 
tionary structure  in  Gogebic  cherts 229 

cited  on  ore  concenti*ation  in  Gogebic  district ..      396 
cited  on  ore  concretions  in  Gogebic  and  Gun- 
flint  Lake  rocks 344 

cited  on   secondary  enlargements  of   mineral 

fragments 80 

cited  on  unconformity  in  Penokee  district 176 

quoted  on  origin  of  dolomites   and  cherts  of 

Penokee  district 231 

J. 

Jackson,  C.  T.,  report  on  mineral  lands,  abstract  of.  43 
reference  to 44 

Janson,  F.  A.,  acknowledgments  to... 34 

analysis  by 348 

Jasper,  definition  of 308 

distinction  between  ore  and 319-320 


INDEX. 


507 


Page. 

Jasper  of  Curry  member J - -  -  33^-335 

of  jaspilite,  Verona  mine,  photomicrograph  of . .      316 

of  Negaunee  formation _ 275-277 

Jasper  band  in  jaspiUte,  Curry  member,  photomi- 
crograph of - 316 

Jasper  bands,  contortions  in,  figure  showing 302 

Jaspilite,  jasper  from,  photomicrograph  of 316 

jasper  band  in,  photomicrograph  of 316 

of  Curry  member 335-337,341-342 

of  Traders  member -.- - 307-320 

of  Vulcan  formation,  folds  in,  view  of 356 

See  also  Traders  jaspilite. 
Jenney,  F.  B.,  reporton  magnetic  analysesof  Mich- 
igan ores,  reference  to 60 

Joint  cracks,  minerals  found  in 388 

Julien,  A.  A.,  and  Brooks,  T.  B.,  catalogue  of  rocks, 

reference  to -  -  - -       60 

Juno  exploration,  ore  deposit  at - -      408 

E. 

Keel  Ridge  mine,  ore  at  — —      374 

ore  from,  analysis  of 382 

ore  deposits  of 424-425 

See  alHo  Old  Keel  Ridge  mine. 

Klondike  shaft,  cherty  rock  near 338 

rock  from .- - --      448 

Lake.    See  next  word  of  nam,e. 

Lake  Superior  iron  ores,  organic  markings  in,  plates 

showing  -  -  - - 118, 120 

Lake  Superior  land  distiict,  map  of  portion  of 48 

Ijake  Superior  region,  map,  geological,  of  part  of  . .       33 

Lake  Superior  sandstone,  age  of 493-494 

character  and  relations  of,-- 31,489-490 

occurrence  of  ..- - 45 

topographical  relations  of.- 126 

unconformity  between  Traders  jaspilite  and, 

view  of 492 

Larsson,  Per,  cited  on  distribution  of  phosphorus 

at  Pewabic  mine 400 

report  on  Chapiniron  mine,  abstract  of 86-87 

Laurentian  system,  comyjosition  of -.-  50-52 

Lavas,  basic,  and  derived  schists,  description  of..  142-144 
Lawton,  C.  D.,  cited  on  mineral  resources  of  Michi- 
gan  -..;.       89 

Leith,  C.  K.,  cited  on  altered  greenalite  rocks 344 

cited  on  deposition  of  gr eenali  te .  - ;352 

cited  on  greenalite  of  Mesabi  district 276 

cited  on  ore  concentration  in  Mesabi  district ...      397 
cited  on  productionof  jaspilite  from  greenalite^      355 

Limestone,  analysis  of,  from  Sturgeon  River 60 

See  also  Hermansville  limestone. 
Lincoln,  A.  T.,  cited  on  contact  between  granite  and 

greenstone 147 

Lingulepis  pinniformis,  occurrence  of 493 

Literature,  abstract  of 41 

Little  Q  ainnesec  Falls,  diorite  at 139-141 

greenstone  at 141-143 

power  at I 133 

rocks  exposed  at _. 95,156-157 

section  northward  from 46 

Log  jam  in  Horserace  Rapids,  view  of 158 

Loretto  mine,  anticline  near 284 

ore  from,  analysis  of 382 

section,  horizontal,  of,  at  first  level 405 

section,  longitudinal,  of _ 406 


Page. 
Loretto  mine,  section,  vertical,  of 405 

Vulcan  formation  near 287 

Loretto  and  Appleton  area,  geological  map  of 404 

Loretto- Appleton  belt,  ore  deposits  in _ 404-406 

Lower  Huronian,  features  of 104 

Lower  Menominee  series,  distribution  of 177 

features  of .-. 21-24 

Lower    Quinnesec    Palls.     See    Little    Quinnesec 

Falls. 
Lower  Twin  Falls,  location  of 160 

rocks  exposed  at.. _ 166 

Ludington  mine,  ore  in,  origin  of 89-92 

M. 

Magnetic  observations  bordering  areas  of  Quin- 
nesec schists  and    Randville  dolomite, 

map  showing 286 

Marquette  district,  equivalency  of  formations  in 

Menominee  district  and _ 65-66 

rocks  in,  sequence  of 107,122 

shipments  from 35 

unconformity  in. - 176 

Mashing,  effect  of 151 

Menominee  district,  geological  map  of,  by  R.  D. 

Irving _ 94 

geological  map  of,  by  T.  B.  Brooks 60 

byT.  B.  Brooks  and  C.  E.  Wright 66 

geological  map  and  sections  of In  pocket 

geological  section  across 52 

limits  of 34 

location  and  area  of _. 19 

relations  to  other  iron-bearing  areas 34 

rocks  in,  sequence  of ._ 107,122 

topogi-aphical  map  of In  pocket 

Menominee  River,  course  and  character  of 126 

fall  and  rapids  in 132-133 

green  schists  and  diorite  on 75-76 

Hanbury  slate  along 472 

map  of  region  between  Felch  Mountain  district 

and 34 

rocks  exposed  along 44, 130 

view  of,  above  Sturgeon  Palls 132 

See  also  Sturgeon  Falls. 
Menominee  trough,  map  showing  position  of,  with 

respect  t^  other  Huronian  troughs 34 

Menominee  tongue,  shape  and  size  of 35 

Mesabi  range,  shipments  from 36 

Mica  in  quartzite  of  Sturgeon  formation 184 

Michigan,  Upper  Peninsula  of,  geological  map  of 

portion  of 54 

Millie  mine,  folding  at -._ 238 

ore  from,  analysis  of _. 382 

Mineral  constituents  of  ores 384-386 

Minerals  associated  with  ores 386-391 

Mirabilite,  occurrence  of 391 

N. 

Negaunee  formation,  distribution  of 274 

features  of -. 273-274 

jasper  in 275-277 

lithology  of -- 275-277 

occurrence  and  character  of 24 

origin  of  name 39, 274 

relation  of  adjacent  formations  to 277-278 

of  Randville  dolomite  to 351-252 

Newett,  G.  A.,  cited  on  mines  and  mineral  statis- 
tics   114,121 


508 


INDEX. 


Page. 

Nicolson,  J.  T.,  and  Adams,  P,  D.,  cited  on  cataclas- 

tic  structure  in  limestone 213 

Nlmick  ore, analysis  of .. - -. 382 

Nodules  in  Eandville  dolomite 210 

Northern  Complex, distribution  of 168 

lithologyof 169-174 

rocks  constituting 167 

sequence  of  rocks  of .- 168 

topography  of .  - 168 

Norway,  dolomite  and  iron  formation  at  -  - -      254 

dolomite  bluffs  between  Quinnesec  and,  view  of      2()8 
ore  deposits  near 428-431 

Norway  fold,  description  of 240-242 

structure  at .' 429 

Norway  mine,  ore  at 85,88 

ore  deposits  at  Cyclops  mine  and 428-431 

rocks  at 72 

section,  vertical,  through  Aragon  mine  and 242 

slate  from,  analysis  of 298 

Norway  pit.  Brier  slate  in,  plate  showing 364 

section,  longitudinal,  through... _ 243 

Norway  and  Aragon  folds,  geological  map  of 428 

sections  through.. - 430 

o. 

Old  Keel  Ridge  mine,  folding  at,  sketch  showing  . . .      357 
ore  deposits  at 423-424 

Ore,  analysis  of,  Chapin,  Quinnesec,  and  Cornell 

mines- _ 383 

analysis  of ,  from  Currymine 348 

from  Traders'  mine 311 

chemical  composition  of - 378-384 

distinction  between  jasper  and 319-320 

effloresence  on _.. 390-391 

lithologyof 373-391 

mineral  constituents  of 384-386 

minerals  associated  with 386-391 

of  Curry  member 335 

photomicrograph  of 316 

of  Ludington  mine,  origin  of 89-92 

of  Menominee  district,  analyses  of 382 

of  Traders  member 309-313 

physical  characters  of 373-378 

specific  gravity  of 379-380 

stratigraphical  occurrence  of 376 

See  also  names  of  mines. 

Ore  bodies,  conditions  necessary  to  formation  of. . .      393 

Ore  breccia,  view  of,  near  contact  of  Traders  mem- 
ber with  Brier  slates,  Currymine 368 

Ore  deposits,  belts  of 404 

character  of -- 28-29 

concentration  of,  time  and  depth  of.. 403 

descriptions  of 404-456 

development  of 395-401 

distribution  and  shape  of 392-394 

formation  of,  manner  of 29 

in  Hanbury  slate 416-488 

topographical  relations  of 401-403 

Organic   markings   in   Lake   Superior   iron   ores, 

plates  showing 118,120 

Orthoceras,  occurrence  of 494 

Orthoclase-paragonite-schist,  analysis  of,  from  Big 

Quinnesec  Palls 5.5 

Orthoclase-porphyroid,  analysis  of,  from  Big  Quin- 
nesec Palls 55 


P. 

Page. 
Paleozoic  sediments,  occurrence  and  character  of . .       31 

Paleozoic  system,  description  of 489-494 

Paleozoic  time,  deposition  in 499-500 

Paragonite-schist,  analysis  of,  from  Big  Quinnesec 

Falls 55 

Patton,  H.  B.,  cited  on  microscopical  study  of  some 

Michigan  rocks 102 

Pegmatite  of  Northern  Complex,  occurrence  of 172 

Penokee  district,  succession  in 122 

unconformity  in 176 

Pewabic  fold,  description  of 239 

Pewabic  mine,  ore  from,  analysis  of .382 

ore  deposits  of 418-420 

section  at _ 106 

section,  horizontal,  of,  at  third  level '  418 

section,  vertical,  through  No.  1  shaft 1 419 

Vulcan  formation  at,  thickness  of 360 

Pewabic  pit,  concentrating  works  at,  view  ot  .'. 368 

Phosphorus  in  Ludington  mine,  distribution  of 89-90 

occurrence  of , 379 

variation  in  amount  of 400-401 

Physiography,  discussion  of 125-129 

Pine  Creek,  coui'se  and  character  of 127 

Sturgeon  quartzite  on.. 184-194 

topography  of  valley  of 201 

Pitching  troughs,  formations  forming 393 

Plains,  description  of 125-126 

Porphyroid,  orthoclase,  analysis  of,  from  Big  Quin- 
nesec Falls 55 

Power,  water,  on  Menominee  River. 133 

Prospect  Bluff,  pre-Cambrian  form  of 129 

Pumpelly,  R.,  cited  on  statistics  ot  mining  indus- 
tries  84 

Putnam,  B.  T.,  cited  on  character  of  ore 375 

report  on  iron  ore  of  Michigan  and  northern 

Wisconsin,  abstract  of 84 

Pyrite,  occurrence  of 388 

Q. 

Quartz,  occurrence  of 386 

of  Curry  member 345 

Quartz-poi*phyry,  analysis  of,  from  Big  Qiiinnesec 

Falls 154 

lithologyof 153 

Quartz  rocks,  cherty,  comparison  of,  with  rocks  of 

Marquette  and  Gogebic  districts 229-230 

in  Randville  dolomite 226-232 

origin  of 230-232 

Quartz-slate  of  Curi'y  member 337 

Quartz  veins  in  Sturgeon  quartzite 185 

Quartzite  at  Falls  of  the  Sturgeon  River 75 

of  Huronian  series 82 

of  Sturgeon  formation 183-185 

of  Traders  member,  photomicrograph  of 316 

of  Vulcan  formation,  photomicrogi*aph  of 316 

See  also  Sturgeon  quartize. 
Quartzite  and  conglomei-ate  in  Traders  member .  ;M)-307 
Quartzites   and   graywackes  of   Hanbury    forma- 
tion....   464-466 

Quinnesec,  dolomite  bluffs  between  Norway  and, 

view  of 208 

folding  near 248 

ore  deposits  at 425-428 

Randville  dolomite  north  and  northeast  of 263, 267 

section  through... 68 


INDEX. 


509 


Page. 

Quinnesec  area,  geological  map  of 426 

Quinnesec  fold,  description  of 239-240 

Quinnesec  mine,  conglomerate  in,  effects  of  pressure 

on --- -      305 

ore  of - --- 87 

analyses  of -- 383, 383 

ore  deposits  at 427 

pre-Cambrian  topography  at 129 

Quinnesec  pit,  unconformity  on  west  side  of,  view  of.      492 
Quinnesec  schist,  composition  and  structure  of,  in 

southern  area 133-134 

distribution  of,  in  southern  area 131-132 

in  western  area 159 

exposures  of 165-167,155-159 

divisions  of 135 

lithology  of ,  in  southern  area 134-155 

in  western  area _ 160-165 

magnetic  observations  bordering  areas  of  Eand- 

ville  dolomite  and,  map  showing _      286 

occurrence  and  character  of 20,130,131 

origin  of,  in  western  area _ _ 165 

origin  of  name 39 

relations  to  overlying  formations 131 

topography  of ,  in  southern  area 132-133 

in  western  area 159-160 

Quinnesec  Valley,  hypothetical  section  across  Me- 
nominee region  near 93 


Raudville  dolomite,  argillaceous  rocks  in 225-226 

cherty  quartz  rocks  in 226-232 

distribution  of 22-24,200-202,203-208 

exposures  of 255-273 

folding  in 23,232-248,369-270 

lithology  of 209-232 

magnetic  observations  bordering  areas  of  Quin- 
nesec schists  and,  map  showing 286 

origin  of  name 39,300 

plate  showing  brecciated 218 

relation  of  basal  member  of  Upper  Huronian 

to 252-254 

of  Hanbury  slate  to 366-370 

of  N  egaunee  formation  to 251-253 

of  Sturgeon  quartzite  to 250-251 

Vulcan  formation  to 361-365 

sandstones  in 210-215 

talcose  schists  in 221-225 

thickness  of 23,248-350 

topography  of 126,301,203,208-209 

view  of,  east  of  Aragon  mine 318 

width  of 203 

R.  28  W.,  T.  37N.,  section9 110 

R.  28W.,  T.  .3SN.. _. 133 

section  4 _ 133 

section  9 177 

section  16 110 

E.  38W.,  T.  39N 57,132 

section  2 34 

section  6 179,186,194 

section  7.. &5, 

74,186,195,201,205,306,273,331,331 
section  8. .. .  65, 93, 179, 187, 196, 200, 305, 351 

section  9 186 

section  10 74 

section  11 34,306 

section  14 34 


Page. 

R. 28  W-.T-SSN., section  15 204,206,307 

section  16 204,305 

section  17 304,305,323 

section  18 204, 205, 207, 308, 372, 333 

section  19... 484 

section  31... 467,484 

section  22.. 57,293,322,453 

section  33 34 

section  36 _ 34 

sections29,  30 476 

section  35 34 

R.38W.,T.40N., sections  28,  29 46 

R.29W.,T.38N 133 

K.29W.,T.39N 56,57 

section  1 179,188 

section  2 183 

sectiou3. 205,206,247 

section  4 70,72,305,306,241 

section  5 305,298,350 

section  6 205, 393, 322, 3a3, 360, 459, 460 

sections  7,8.. 478 

section  9 205, 2.54, 267, 374, 2*3, 

304, 330, 350, 351, 358, 363, 368, 434, 439, 440 

section  10 305, 346, 385, 338, 439, 440, 449 

section  11... 60, 

305, 306, 307, 246, 247, 385, 450, 453 
section  13.  305, 306, 335, 249, 271, 272, 461, 462 

section  1.3- 73, 

271, 373, 316, 323, Sas, 461, 463, 475, 484 

section  14 453 

section  17 483 

section  35 360 

section  36 76,110,388,484 

section  37.. 58,68 

section  35.. 110 

R.  29  W.,  T.  40  N 74 

section  32 74, 

128, 201, 202, 227, 356, 369, 480, 481 

section  33 138,300,351,480,481 

section  34 201 

R.  29W.,  T.  41N.. 34,185,186 

section  39 174,178 

section  31.. 174,189,190,193 

section  33. 174, 179, 189, 190, 191 

R.  30  W.,  T.  39  N 44,45 

section  1.. 30.5, 393,  a33, 458 

section  3 178,305, 

306, 340, 263, 264, 385, 394, 333, 366, 458, 459 

section  3 240,263,322 

section  5 429,431 

section  6 458 

sections 428,439,431 

section  9. 438 

section  11 477 

section  12 _ 110 

section  14 46 

section  35 458 

R.  30W.,  T.  40N 45,46,56,59,110,185,186 

section  1 174 

section  3 101, 174, 177, 186, 1»9, 190, 193 

section  3 193,200,301,351,255 

section  11 14 

section  13 174 

section  14 310,255,287,393,331,331 

section  15 159,389,476 

section  19 465 


510 


INDEX. 


Page. 

B.30  W.,T. 40  N., sections  30,  21 201,234 

section  22 -... 201,256,287 

section  23 201 

section  24 -. 58 

section  25 58,201,286,321,413 

section  26 201 

section  27 201,20) 

sections  28,39 205 

section  30 44,46,204,205,210,248 

section  31 205 

section  33. 205, 

237, 33:3, 361, 263, 333, 357, 379, 423, 424, 490 

section  33. 205, 233, 261 ,  263, 458, 457 

section  34 46, 178, 205. 2:»,  363, 364, 294 

section  35 46,72,178, 

205, 206, 220, 225, 389, 247, 263, 264, 265, 458 

section  .36 205,458 

R.:»W.,T.  41N 34,44 

section  12 101 

R.  30W,  T.  42N.. 34 

section  35 46 

R.  31  W.,  T.  39N 45 

B.  31  W.,  T.  40N 44,46,131 

section  12 160 

section  13 389,471 

section  23 205 

section  24 305,465 

section  35 57, 

304, 205, 207, 208, 2a5, 294, 464, 456, 467 

section  26 205,323,454,4.56 

R.31  W.,  T.  41  N.,  section  17. 110 

E.31  W.,  T.  43  N., section  4 108 

R.  31  ^.,1. 44  N., section  33 108 

Rapids  and  falls  in  Menominee  River _  133-133 

Relief,  features  of 125-126 

Riggs,  R.  B.,  analysis  by.. 138,143,146,152,153,154 

Rivers,  course  and  character  of 126-137 

Rock  dam.  Sturgeon  quartzite  at 189-194 

Rocks,  classification  of 38-39 

Rominger,  C,  cited  on  Herraansville  limestone 494 

cited  on  Lake  Superior  sandstone 489, 493 

cited  on  rocks  at  the  Falls  of  the  Sturgeon 198 

reference  to.. 41 

report  on  geology  of  Upper  Peninsula  of  Michi- 
gan, abstract  of 109-111 

report  on  Menominee  iron  region,  abstract  of. .  71-78 

report  on  Paleozoic  rocks,  abstract  of 60 

work  of 36 


Saginaw  mine,  rocks  at 73 

San  Jose  ore,  analysis  of 382 

Sanders,  G.  N.,  reports  by,  reference  to 42,43 

Sandstones,  dolomitic,  in  Randville  formation  ...  210-215 

Sandstone,  removal  of,  from  valleys 138 

See  also  Lake  Sttperior  sandstone. 

Saussurite-gabbro,  occurrence  of 155 

Schist,  alteration  of  gabbro  to. 138-139 

analysis  of,  from  Little  Quinnesec  Falls 146 

at  Sturgeon  Falls,  Uthology  of 137-138 

derived  from  diorite  at  Little  Quinnesec  Falls. .      140 
See  aUo  Quinnesec  schists. 

Schist,  basic,  occurrence  of 156 

origin  of 148-149 

Schist,  fragmental,  in  western  area  of  Quinnesec 

schists 164-165 

Schist,  gi'een,on  Menominee  River... 75-76 


Page. 

Schist,  talcose,  analysis  of,  from  Aragon  mine. 332 

in  Randville  dolomite -. 221-335 

Schistose  felsites,  lithology  of 154 

Schistose  structure  in  dolomites. 213-214 

Schistosity  of  fine-grained  greenstones,  origin  of . . .      143 

Sericite  in  quartzite  of  Sturgeon  formation 184 

Sericite-schist,  lithology  of 154 

occurrence  of. 155,156,157 

Sericite-slates  of  Hanbury  formation 46.3-464 

Sei'pentine,  analysis  of,  from  Chapin  ore. 390 

occurrence  of 389 

Shipments,  amount  of 35-36 

Silica,  abstraction  of 400 

occuiTence  of 378 

Slate,  analysis  of,  from  Traders  member 298 

of  Randville  dolomite 366 

of  Traders  member 39.5-300 

See  also  Brier  slates;  Hanbury  slate. 
Slates,  calcareous,  and  dolomites  of  Hanbury  for- 
mation   466-467 

Slates,  clay,  of  Hanbury  formation 463-464 

Smyth,  H.  L.,  report  on  relations  of  Lower  Menom- 
inee and  Lower  Marquette  series,  ab- 
stract of 107-109 

Smyth,  H.  L.,  and  Clements,  J.  M.,  cited  on  Crystal 

Falls  district... 34 

cited  on  geology  of  Felch  Mountain  range .56 

cited  on  Sturgeon  quartzite  and  Randville  dolo- 
mite  39 

cited  on  Sturgeon  quartzite  of  Felch  Mountain 

district 177 

report  on  Crystal  Falls  district,  abstract  of  . .  116-121 

Specific  gravity  of  ores 379-380 

Steiger,  George,  analysis  by 222,479 

Streams,  course  and  character  of 126-127 

Structure,  relation  of  topography  to l26 

Sturgeon  Falls,  exposures  near,  map  showing 288 

gabbroat 136-138 

greenstone-schists  at 95 

rocks  exposed  at 155-156 

section  through 58 

view  from... 132 

Sturgeon  Mills,  Hanbury  slate  near 475^76 

Sturgeon  qiiartzite,  arkoses  and  graywackes  in . .  181-182 

conglomerates  in 179-181 

dikes  and  veins  in 185-186 

distribution  of 21-22,177-178 

exposures  of 189-199 

folding  of 21,186-187 

gray  wackes  and  arkoses  in 181-182 

lithology  of 179-186 

map  of  exposures  near  contact  of  Archean  com- 
plex and 186 

origin  of  name 39,177 

quartzite  in 18;3-1H5 

relations  of  Randville  dolomite  to 250-251 

of  underlying  formations  to 188-189 

thickness  of 187-188 

topography  of 22,178 

veins  and  dikes  in.. 185-186. 

Sturgeon  River,  course  and  character  of 136-137 

Falls  of  the,  conglomerate  at 50,94 

conglomerate  and  quartzite  at 187 

quartzite  at 183 

quartzite  and  granite  at 75 

rocks  exposed  at 66 

section  at 51 


INDEX. 


511 


Page. 
Sturgeon  River,  Falls  of  the,  sketch  map  of  expo- 
sures at 195 

Sturgeon  quartzite  at 196-199 

RandTillo  dolomite  in  valley  of 271-273 

section  through 68 

Sulphur,  occurrence  of _ 379 

Swank,  J.  M. ,  cited  on  production  of  iron  ores 81 


Talc, analysis  of,  from  Chapin  ore 390 

occurrence  of 390 

Talcose  schist,  analysis  of,  from  Aragon  mine. 323 

in  Randville  dolomite 221-325 

Topography  of  district,  features  of 19,125-126 

of  district, origin  of.. 137-129 

pre-Cambrian  features  of 129 

relation  of  structiire  to 126 

of  Han  bury  slate .-. 463 

of  Northern  Camplex 168 

of  Quinnesec  schists  in  southern  area 133-133 

in  western  area 159-160 

©f  Kandville  dolomite 301,203,208-209 

of  Sturgeon  quartzite 178 

291 
184 
110 
132 
177 
110 
133 


T.39N. 


T.  39N 


of  Viilcan  formation... 

Tourmaline  in  quartzite  of  Sturgeon  formation. 

T.  37  N.,  R,  28  W.,  section  9 

T.  38  N.,  R.  28  W.,  section  4 

section  9 

section  16 

T.  38  N.,  R.  29  W 

T.  39N.,  R.  28  W 57,132 

section  3 34 

section  6 179,186,194 

section  7 65, 

74, 186, 195, 201, 205, 206, 272, 321 , 331 
section  8 . . . .  65, 93, 179, 187, 196, 200, 205, 251 

section  9. 186 

section  10 74 

section  11.. 34,206 

section  14 34 

section  15 204,206,207 

section  16 204,205 

section  17 204,205,332 

section  18 304,305,207,208,272,322 

section  19 484 

section  21 467,484 

section  22 57,293,322,453 

sections  23,  26 _■ 34 

sections  29,  30 476 

section  35- 34 

T.  39  N.,  R.  29W 58,57 

section  1 179,188 

section  2 183 

sections 205,206,347 

section  4 70,73,205,206,241 

section 5 205,398,350 

section  6 205,393,323,333,360,4.59,460 

sections  7,  8 478 

section  9 205,254,267,274,293, 

304, 330, 350, 351, 358, 362, 368, 4.34, 4.39, 440 

section  10 205, 246, 285,  .338, 439, 440, 449 

section  11..  60,205,206,207,247,285,450,453 
section  12 .  205, 206, 225, 349, 271, 372, 461, 462 

section  13 72, 

271,272,316,322,333,461,462,475,484 

section  14.. 453 

section  17 483 


T.  39N 
T.  40N 
T.  40N 


T.40N, 


T.  40  N 


T.  41N. 
T.  41  N. 


T.  41  N, 


T.  41  N. 
T.  42  N. 


Page. 

,  R.  29  W., section  25... m) 

section  36 76,110,388,484 

section  27 58,68 

section  35 110 

,  R.  .30W. 44,45 

sectionl 305,293,333,458 

section  2 178, 

205, 206, 263, 284, 285, 294, 332, 366, 458, 459 

section  3.. 363,323 

section  5 439,431 

sections 458 

section  8. 428,429,431 

section  9 428 

section  11 477 

section  12. -. 110 

seotionU •    46 

section  35 458 

,  R.  31  W 45 

,  R.  28  W.,  sections  28,  29 46 

,  R.  29W 74 

section  32... 74, 

128, 201, 202,227, 334, 2,36, 256, 369, 480, 481 

section  33 128,200,261,480,481 

section  34 201 

,  R.  30  W... 45,46,56,59,110,185^186 

sectionl. 174 

section  2..  101,174,177,186,189,190,192,340 

sections 19.3,200,201,240,351,355 

section  11 200 

.section  12 174 

section  14 200,310,255,287,292,321,331 

section  15 159,289,476 

section  19 465 

sections 20,  21 334,236 

section  23 201,256,287 

section  23. 201 

.section  24.. 58 

section  25.. ._  58,201,286,321,413 

section  26 201 

section  27 201,205 

sections28,  29.. 205 

section  30 44,46,204,305,310,248 

sections! 205 

section  33 205, 

337, 233, 361 ,  3&3, 323, 357, 379, 423, 434, 490 

section  Si 205, 233, 261, 263, 456, 457 

section  34. 46, 178, 305, 2.39, 363, 264, 294 

section  35 46,72,178, 

205, 206, 220, 225, 239, 247, 263, 264, 2&5, 458 

section  36... 205,458 

,  R.  31  W 44,45,131 

section  13. 160 

section  13.. 389,471 

section  33 205 

section  24. 205,465 

section  35 57, 

204,20.5,207,208,235,294,454,456,457 

section  26 205,323,454,456 

,  E.  27  W.-- 34 

•  R.  asW 34,185.186 

section  29 174,178 

section  31 174,189,190,193 

section  32 174, 179, 1S9, 190, 191 

,R.  SOW 34,44 

section  12 101 

,  R.  31  W.,  section  17 no 

,  R.  SOW _ 34 


512 


INDEX. 


Page. 

T.  42  N.,R. 30  W., section  a5 ^ 

T. «  N.. R. 31 W., section  4. 108 

T.  44  N.,E.  31 W., section  33. 108 

Traders  jaspilite,  folds  in,  view  of - 256 

unconformity  between  Lake  Superior  sandstone 

and,  view  of -      492 

Traders  member  of  Vulcan  formation,  conglomer- 
ate and  quartzite  in  - 300-307 

deposition  of - ai2-35o 

distribution  of 291-394 

jaspilite  in 307-320 

lithologyof 294-320 

occurrence  and  character  of 25 

ore  breccia  near  contact  of  Brier  slates  and, 

view  of 368 

origin  of  name -- 40, 291 

quartzite  of,  photomicrograph  of 316 

quartzite  and  conglomerate  in 300-307 

relation  of  Brier  slatesto 349-350 

slates  of 295-300 

thickness  of - -  -      *^ 

See  also  Vulcan  formation. 
Traders  mine,  folds  in  Trader.s  jaspilite  in,  view  of.      256 

geological  map  of  Cornell  mine  and 406 

jaspilite  at,  sketch  showing  puckering  of 3.')8 

ore  from,  analysis  of -  311,382 

ore  deposit  in 407-410 

rock  at _. 306-30* 

Traders  member  at,  description  of 292 

thickness  of 360 

Vulcan  formation  near 286 

Traders-Forest  belt,  ore  deposits  of 407-411 

Tuffs,  basic,  and  derived  schists,  description  of  . .  144-145 

Twin  Falls,  greenstone  at 97 

rocks  exposed  at -      163 

section  near 69 

See  Upper  Twin  Falls;  Lower  Twin  Palls. 

XJ. 

Unconformity  between  Traders  jaspilite  and  Lake 

Superior  sandstone,  view  of 492 

Upper  Hm'onian,  featuresof... 104 

relation  of  Randville  dolomite  to  basal  member 

of 252-254 

Upper  Menominee  series,  description  of 280-487 

character  and  occurrence  of 24-31,280-285 

folding  in.. - 284 

formations  composing 280 

separation    from    overlying    and    underlying 

rocks 280-283 

Upper  Qulnnesec  Falls.    See  Big  Quinnesec  Palls. 
Upper  Twin  Palls,  basin  below  and  barrier  rock 

at,  views  of 160 

fragmental  schists  at 164 

greenstone  at,  view  of.. 162 

location  of... 160 

rocks  exposed  at 161,166 

V. 

Valleys,  rocks  occurring  in 126 

Van  Hise,  C.  R. .cited  on  classification  of  ore  deposits.  395 

cited  on  concretions  in  Marquette  jaspilite 344 

cited  on  definition  of  jaspilite 308 

cited  on  development  of  ore  deposits 403 

cited  on  direction  of  joints 258 

cited  on  formation  of  chert 354 

cited  on  iron  ores  of  Marquette  district 100 


Page. 
Van  Hise,  C.  R..  cited  on  iron-ore  deposits  of  Me- 
nominee district 124 

cited  on  pre-Cambrian  North  American  litera- 
ture   109.113-114 

cited  on  principles  of  North  American  pre-Cam- 
brian geology 114 

cited  on  unconformities 372 

correlation  paper  on  Archean  and  Algonkian, 

abstract  of 99-100 

letter  of  transmittal  by 17 

quoted  on  origin  of  jaspilite 353-355 

report  on  pre-Cambrian  geology  of  Lake  Su- 
perior region,  abstract  of 103-104 

report  on  Lake  Superior  stratigraphy,  abstract 

of.. 98-99 

Van  Hise,  C.  R.,  and  Bayley,  T,".  S.,  cited  on  altera- 
tion of  carbonate  83 

cited  on  cherts  of  Marquette  district 2.30 

cited  on  literature  on  pre-Cambrian  of  Lake 

Superior  region.. 99 

cited  on  Marquette  district 115 

cited  on  Negaunee  formation  of  Marquette  dis- 
trict  230,277 

cited  on  concentration  of  ore,  Marquette  district      396 

cited  on  petrography  of  Archean  complex 40 

cited  on  pre-Cambrian  formations 42 

cited  on  slates  of  Kona  dolomite 266 

cited  on  structure  at  Chapin  mine 423 

quoted  on  origin  of  dolomites  and  cherts  of  Pe- 

nokee  district 231 

report  on  Marquette  district,  abstract  of 112-113 

report  on  Menominee  district,  abstract  of 121-124 

Van  Hise,  C.  R.,  and  Irving,  R.  D.,  cited  on  concre- 
tionary structure  in  Gogebic  cherts 229 

cited  on  ore  concentration  in  Gogebic  district . .      396 
cited  on  ore  concretions  in  Gogebic  and  Gun- 
flint  Lake  rocks 344 

cited  on   secondary  enlargements  of   mineral 

fragments 80 

cited  on  unconformity  in  Penokee  district 176 

Veins  and  dikes  in  Sturgeon  quartzite 185-186 

Vermilion  range,  shipments  from 36 

Verona  area,  geological  map  of  East  Vulcan  area 

and. 450 

Verona  mine,  jasper  from  jaspilite  of,  photomicro- 
graph of 316 

ore  deposits  of 453 

Vivian  mine,  ore  deposit  at 428 

Vulcan,  Menominee  tongue  at,  width  of 35 

Vulcan  formation,  brecciation  of 362 

brier  slate  of 320-331 

conglomerates  and  quartzites  in 300-307 

Curry  member  of 331-349 

deposition  of 26-27 

distribution  of 285-290 

Hanbury  formation  and,  explanation  of  ..  370-372 

exposures  of 4.56-461 

folding  in 556-359 

genesis  of.. 352-355 

jaspilites  in  Traders  member  of 3 J7-320 

jaspilites  in,  view  of  folds  in 356 

members  of 25,291-351 

relations  between 349-351 

occuiTence  and  features  of 24-29 

origin  of  name 39 

quartzite  at  base  of,  photomicrograph  of 316 

quartzites  and  conglomerates  in 300-307 


INDEX. 


513 


Vulcan  formation,  relation  of  HanTsTiry  slates  to.  365-366 

relation  of  Randville  dolomite  to 361-3H5 

rocks  of,  micropliotograplis  of 31 1> 

section  across _ _ 4a5 

thickness  of 27,359-361 

topography  of 126,301 

Traders  member,  distribution  of 291-294 

See  also  Brier  slate;  Curry  member;  Traders 
member. 

Vulcan  mine,  ore  at,  character  of 84 

"Wadsworth,  M.  E.,  cited  on  conglomeratic  green- 
stone at  Little  Quinnesec  Falls 156 

cited  on  definition  of  jaspilite 308 

cited  on  origin  of  basic  schists  at  Little  and  Big 

Quinnesec  Falls 141 

report  on  iron,  gold,  and  copper  districts,  ab- 
stract of.. ._...  101-102 

Wadsworth,  M.  E,,  and  Whitney,  J.  D.,  cited  on 
Azoic  system  and  its  proposed  subdivi- 
sions.. 80 

Walcott,  C.  D. ,  cited  on  fossil  MedusBB 354 

cited  on  intraf ormational  conglon^erates  in  Pa- 
leozoic rocks - 219 

cited  on  Lake  Supei*ior  sandstone 493 

"Walpole  fold,  description  of 238-239 

"Walpole  mine,  ore  .^rom,  analysis  of 382 

ore  deposits  of 414-417 

section,  horizontal,  of,  at  third  level 417 

Walpole-Chapin  fold,  shafts  on,  view  showing 416 

Water  power  on  Menominee  River 133 

Waucedah ,  geological  map  of  yicinity  of 453 

ore  deposits  at 453-455 

Randville  dolomite  near,  boundary  of 208 

Weidman ,  Samuel,  assistance  by 33 

West  Paulet,  Vt.,  slate  from,  analysis  of 298 

West  Vulcan  area,  geological  map  of  Central  Vul- 
can area  and  portion  of 438 

West  Vulcan  folds,  description  of ...  ^ 245-346 

West  Vulcan  mine.  Brier  slate  at,  sketch  showing 

folding  in 358 

calcite  crystals  in 387 

cherty  rock  near 338 

geological  map  of  vicinity  of... 434 

ore  deposits  of 439-448 

section,  horizontal,  of,  at  eighth  level 441 

at  fifteenth  level 447 

at  thirteenth  level 445 

at  twelfth  level 444 

section,  vertical,  of.  near  Burnt  shaft .- 446 

through  Burnt  shaft 443 

through  No.  2  shaft 442 

Whitney,  J.  D.,  reference  to _ 41 


Page. 
Whitney,  J.  D.,  and  Foster,  J.  W.,  report  on  age  of 

Lake  Superior  sandstone,  abstract  of 45 

report  on  Lake  Superior  land  district,  abstract 

of.. - 45-48 

Whitney,  J.  D.,  and  Wadsworth,  M.  E.,  cited  on 
Azoic  system  and  its  proposed  subdi- 
visions        80 

Whittlesey,  Charles,  report  on  origin  of  Azoic  rocks 

of  Michigan  and  Wisconsin,  abstract  of.        49 
Wichmann,  Arthur,  report  on  iron-bearing  rocks 

soiith  of  Lake  Superior,  abstract  of 68 

Wniiama,  G.  H.,  cited  on  andesine  in  granite- 
porphyry  152 

cited  on  chlorite-schist  derived  from  diorite 140 

cited  on  contacts  between  chlorite-schists  and 

massive  greenstones 163 

cited  on  crystalline  rocks 103 

cited  on  gabbro  at  Sturgeon  Fails 136 

cited  on  granititc  and  quartz-porphyry 153 

cited  on  lithology  of  Qxiinnesec  schists 134 

cited  on  magnetite  and  rutile  in  rocks  at  Big 

Quinnesec  Falls 158 

cited  on  petrography  of  greenstone-.schists 40 

cited  on  schist  from  Little  Quinnesec  Falls 146 

quoted  on  diorite  at  Little  Quinnesec  Falls.  139-140, 157 
quoted  on  fragmental  rock  at  Upper  Twin  Falls.      164 

quoted  on  gabbro  at  Sturgeon  Falls 137,138 

quoted  on  gi-eenstone  at  Fourf oot  Falls 1 63 

quoted  on  greenstone  at  Little  Quinnesec  FaUs.     141, 

142-143. 

quoted  on  origin  of  basic  schists. 149 

reference  to 136 

report  on  greenstone-schist  areas  of  Menominee 

and  Marquette  districts,  abstract  of 94-98' 

Winchell,  A., report  by,  reference  to _ _._       49' 

Winchell,  H.  V.,  cited  on  history  of  mineral  depos- 
its in  Lake  Superior  iron  region 107 

Winchell,  N.  H.,  cited  on  crystalline  rocks  of  the 

Northwest '   80 

report  on  origin  of  Archean  greenstones,  ab- 
stract of 111-112 

cited  on  supposed  pre-Taconic  organisms 114 

■  report  on  crystalline  rocks,  abstract  of 101 

Winchell,  N.  H.  and  H.  V.,  cited  on  possible  chem- 
ical origin  of  the  iron  ores  of  the  Kee- 

watin  in  Minnesota 89 

Wisconsin  granite,  relation  to  acid  intrusives 14a 

Wright,  C.  E.,  report  on  geology  of  Menominee  iron 

region,  abstract  of 69-71 

report  on  mineral  statistics,  reference  to 62; 

reference  to 41,61 

work  of 36, 

Wright,  C.  E.,  and  Brooks,  T.  B.,  geological  map  of 

Menominee  iron  region  by 66 


0 


MON    XLVI — 04- 


-33 


PUBLICATIONS  OF  UNITED  STATES  GEOLOGICAL  SURVEY. 

[Monograph  XLVI.] 

The  serial  publications  of  the  United  States  Geological  Survey  consist  of  (1) 
Annual  Reports,  (2)  Monographs,  (3)  Professional  Papers,  (4)  Bulletins,  (5)  Mineral 
Resources,  (6)  Water-Supply  and  Irrigation  Papers,  (7)  Topographic  Atlas  of  the 
United  States — folios  and  separate  sheets  thereof,  (8)  Geologic  Atlas  of  the  United 
States — folios  thereof.  Tlie  classes  numbered  2,  7,  and  8  are  sold  at  cost  of  publica- 
tion; the  others  are  distributed  free.  A  cii'cular  giving  complete  lists  may  be  had 
on  application. 

MONOGRAPHS. 

I.  Lake  Bonneville,  bv  G.  K.  Gilbert.     1890.     4°.     xx,  438  pp.     51  pi.     1  map.     Price  $1.50. 

(Out  of  stock.) 
II.  Tertiary  history  of  the  Grand  Caiion  district,  with  atlas,  by  C.  E.  Button,  Capt.,  U.  S.  A. 

1882.  4°.     xiv,  264  pp.     42  pi.  and  atlas  of  24  sheets  folio.     Price  SIO. 

III.  Geology  of  the  Comstock  lode  and  the  Washoe  district,  with  atlas,  by  G.  F.  Becker.     1882. 

4°.     XV,  422  pp.     7  pi.  and  atlas  of  21  sheets  folio.     Price  111. 

IV.  Comstock  mining  and  miners,  by  Eliot  Lord.     188.S.     4°.     xiv,  451  pp.     3  pi.     Price  $1.50. 
V.  The  copper-bearing  rocks  of  Lake  Superior,  by  R.  D.  Irving.     1883.     4°.     xvi,  464  pp.    15  1. 

29  pi.  and  maps.     Price  $1.85.     (Out  of  stock.) 
VI.  Contributions  to  the  knowledge  of  the  older  Mesozoic  fiora  of  Virginia,  by  W.  M.  Fontaine. 

1883.  4°.     xi,  144  pp.     54  1.     54  pi.     Price  $1.05. 

VII.  Silver-lead  deposits  of  Eureka,  Nevada,  bv  J.  S.  Curtis.     1884.     4°.     xiii,  200  pp.     16  pL 
Price  $1.20. 
VIII.  Paleontology  of  the  Eureka  district,  by  C.  D.  Walcott.    1884.    4°.    xiii,  298  pp.    24  1.    24  pi. 
Price  .$1.10. 
IX.  Brachiopoda  and  Lamellibranchiata  of  the  Raritan  clays  and  greensand  marls  of  New  Jersey, 
by  R.  P.  Whitfield.     1885.     4°.     xx,  .338  pp.     35  pi.     1  map.     Price  $1.1.5. 
X.  Dinocerata.     A  monograph  of  an  extinct  order  of  gigantic  mammals,  by  O.  C.  Marsh.     1886. 

4°.     xviii,  243  pp.     56  1.     56  pi.     Price  $2.70. 
XI.  Geological  history  of  Lake  Lahontan,  a  Quaternary  lake  of  northwestern  Nevada,   by  I.  C. 
Rus.sell.     1885.     4°.     xiv,  288  pp.     46  pi.  and  maps.     Price  $1.75. 
XII.  Geology  and  mining  industry  of  Leadville,  Colorado,  with  atlas,  by  S.  F.  Emmons.     1886. 
4°.     xxix,  770  pp.     45  pi.  and  atlas  of  35  sheets  folio.     Price  $8.40. 

XIII.  Geology  of  the  quicksilver  deposits  of  the  Pacific  slope,  with  atlas,  by  G.  F.  Becker.     1888. 

4°.     xix,  486  pp.     7  pi.  and  atlas  of  14  sheets  folio.     Price  $2. 

XIV.  Fossil  fishes  and  fossil  plants  of  the  Triassic  rocks  of  New  Jersey  and  the  Connecticut  Valley, 

by  J.  S.  Newberry.     1888.     4°.     xiv,  152  pp.     26  pi.     Price  $1. 
XV.  The  Potomac  or  younger  Mesozoic  flora,  by  W.  M.  Fontaine.     1889.     4°.     xiv,  377  pp.     180 

pi.     Text  and  plates  bound  separately.     Price  $2.50. 
XVI.  The  Paleozoic  fishes  of  North  America,  by  J.  S.  Newberry.     1889.     4°.     340  pp.     53  pL 

Price  $1.00. 
XVII.  The  flora  of  the  Dakota  group,  a  posthumous  work,  by  Leo  Lesquereux.     Edited  bv  F.  H. 
Knowlton.     1891.     4°.     400  pp.     66  pi.     Price  $1.10. 
XVIII.  Gasteropoda  and  Cephalopoda  of  the  Raritan  clays  and  greensand  marls  of  New  Jersey,  by 
R.  P.  Whitfield.     1891.     4°.     402  pp.     50  pi.     Price  $1. 
XIX.  The  Penokee  iron-bearing  series  of  northern  Wisconsin  and  Michigan,  by  R.  D.  Irving  and 

C.  R.  Van  Hise.     1892.     4°.     xix,  .534  pp.     Price  $1.70. 
XX.  Geology  of  the  Eureka  district,  Nevada,  with  an  atlas,  by  Arnold  Hague.     1892.     4°.     xvii, 
419  pp.     8  pi.     Price  $5.25. 
XXI.  The  Tertiary  rhvnchophorous  Coleoptera  of  the  United  States,  by  S.  H.  Scudder.     1893.     4°. 

xi,  206  pp.     12  pi.     Price  90  cents. 
XXII    A  manual  of  topographic  methods,  bv  Henry  Gannett,  chief  topographer.     1893.     4°.     xiv, 
300  ^ip.     18  pi.     Price  $1. 
XXIII.  Geology  of  the  Green  Mountains  in  Massachusetts,  by  Raphael  Pumpelly,  T.  N.  Dale,  and 
J.E.Wolff.     1894.     4°.     xiv,  206  pp.     23  pi.     Price  $1.30. 


II 


PUBLICATIONS    OF    UNITED    STATES    GEOLOCHCAL    SURVEY. 


XXIV. 

XXV. 

XXVI. 

XXVII. 

XXVIII. 

XXIX. 

XXX. 
XXXI. 

XXXII. 

XXXIII. 

XXXIV. 

XXXV. 

XXXVI. 

XXXVII. 

XXXVIII. 
XXXIX. 

XL. 

XLI. 

XLII. 
XLIII. 
XLIV. 

XLV. 

XLVI. 


^lollusca  and  Crustacea  of  the  Miocene  formations  of  New  Jersey,  bv  R.  P.  Whitfield. 

18W.     4°.     193  pp.     2-4  pi.     Price  90  cents. 
The  Glacial  Lake  Agassiz,  bv  Warren  Upham.     1895.     4°.     xxiv,  6.58  pp.     38  pi.     Price 

$1.70. 
Flora  of  the  Ambo}'  clavs,  bv  J.  S.  Xewberrj-;  a  posthumous  work,  edited  bv  Arthur 

Hollick.     189.^.     4°.     260  pp.     58  pi.     Price  §1. 
Geology  of  the  Denver  Basin  in  Colorado,  bv  S.  F.  Emmons,  AVhitman  Cross,  and  G.  H. 

Eldridge.     1896.     4°.     556  pp.     31  pi.     Price  81.50. 
The  Marquette  iron-bearing  district  of  Michigan,  with  atlas,  by  C.  E.  Van  Hise  and  W.  S. 

Bayley,  including  a  chapter  on  the  Republic   trough,   hy"  H.  L.  Smyth.     1897.     4°. 

608  pp.     35  pi.  and  atlas  of  39  sheets  folio.     Price  85.75. 
Cxeology  of  old  Hampshire  County.  jNIassachusetts,  comprising  Franklin,  Hampshire,  and 

Hampden  counties,  bv  B.  K.  Emerson.     1898.     4°.     xxi,  790  pp.     35  pi.     Price  81-90. 
Fossil  Medusie,  by  C.  D".  Walcott.     1898.     4°.     ix,  201  pp.     47  pi.     Price  81.50. 
Geologv  of  the  Aspen  mining  district,  Colorado,  with  atlas,  bv  J.  E.  Spurr.     1898.     4°. 

XXXV,  260  pp.     43  pi.  and  atlas  of  30  sheets  folio.     Price  83.60. 
Geology  of  the  Yellowstone  National  Park,  Part  II,  descriptive  geologv,  petrography,  and 

paleontology,  bv  Arnold  Hague,  J.  P.  Iddings,  W.  H.  Weed,  C.  D.  Walcott,  G.  H.  Girty, 

T.  W.  Stanton,  and  F.  H.  Knowlton.     1899.     4°.     xvii,  893  pp.     121  pi.     Price  82.45. 
Geology  of  the  Narragansett  Basin,  by  X.  S.  Shaler,  J.  B.  Woodworth,  and  A.  F.  Foerste. 

1899.     4°.     XX,  402  pp.     31  pi.     Price  81. 
The  glacial  gravels  of  Maine  and  their  associated  deposits,  by  G.  H.  Stone.     1899.     4°. 

xiii,  499  pp.     52  pi.     Price  81.30. 
The  later  extinct  floras  of  Xorth  America,  by  J.  S.  Xewberrv;  edited  by  Arthur  Hollick. 

1898.     4°.     xviii,  295  pp.     68  pi.     Price  81.25. 
The  Crystal   Falls   iron-bearing  district  of    Michigan,   by  J.   M.  Clements   and   H.   L. 

Smyth;  with  a  chapter  on  the  Sturgeon  River  tongue,  bv  W.  S.  Bayley,  and  an  intro- 
duction by  C.  R.  Van  Hi.se.     1899.     4°.     xxxvi,  512  pp.  '  53  pi.     Price  82. 
Fossil  flora  of  the  Lower  Coal  Measures  of  JMissouri,  bv  David  White.     1899.     4°.     xi,  467 

pp.     73  pi.     Price  81.25. 
The  Illinois  glacial  lobe,  by  Frank  Leverett.     1899.     4°.     xxi,  817  pp.    24  pi.    Price  81.60. 
The  Eocene  and  Lower  Oligocene  coral  faunas  of  the  United  States,  with  descrij^tions  of 

a  few  doubtfully  Cretaceous  species,  bv  T.  W.  Vaughan.     1900.     4°.     263  pp.     24  pi. 

Price  81.10. 
Adephagous  and  clavicorn  Coleoptera  from  the  Tertiary  deposits  at  Florissant,  Colorado, 

with  descriptions  of  a  few  other  forms  and  a  systematic  list  of  the  non-rhvncophorous 

Tertiary  Coleoptera  of  North  America,  by  S.  H.  Scudder.     1900.     4°.     148"  pp.     11  pis. 

Price  80  cents. 
Glacial  formations  and  drainage  features  of  the  Erie  and  Ohio  basins,  bv  Frank  Leverett. 

1902.     4°.     802  pp.     26  pis.     Price  81.75. 
Carboniferous   ammonoids  of  America,   by  J.  P.  Smith.     1903.      4°.     211  pp.     29  pis. 

Price  85  cents. 
The  Mesabi  iron-bearing  district  of  Minnesota,  by  C.  K.  Leith.     1903.     4°.     316  pp.     33 

pis.     Price  81.50. 
Pseudoceratites  of  the  Cretaceous,  by  Alpheua  Hyatt,  edited  by  T.  W.  Stanton.     1903. 

4°.     351  pp.     47  pis.     Price  81.00. 
The  Vermilion  iron-bearing  district  of  Minnesota,  with  atlas,  b}' J.  M.  Clements.     1903. 

4°.     463  pp.     13  pis.     Price  83..50. 
The  Menominee  iron-bearing  district  of  Michigan,  by  W.  S.  Bayley.     1904.     4°.     513  pp. 

43  pis.     Price  81-75. 


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and  postage  stamps  can  not  be  accepted.     Correspondence  should  be  addressed  to 

The  Director, 

United  States  Geological  Survey. 

Washington,  D.  C. 
January,  1904. 


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card,  but  the  additional  numbers,  as  received,  should  be  added  to  the  first 
entry.] 


Bayley,  William  Shirley. 

.  .  .  The  Menominee  iron-bearing  district  of  Michigan, 
b}^  William  Shirley  Bayley.  Charles  Richard  Van  Hise, 
geologist  in  charge.  Washington,  Gov't  print,  off., 
1904. 

513,  III  p.  4.3  pi.  (incl.  maps,  2  in  pocket),  54  fig.  30J  x  23™'.  (U.  S. 
Geological  survey.     Monographs  v.  46. ) 

"Bibliography  and  abstract  of  literature"  :  p.  41-124. 


Bayley,  ^A^illiam  Shirley. 

.  .  .  The  Menominee  iron-bearing  district  of  Michigan, 
by  William  Shirley  Bayley.     Charles  Richard  Van  Hise, 
I    geologist    in    charge.      Washington,   Gov't    print,    off., 
I     1904. 

513,  III  p.     43  pi.  (incl.  maps,  2  in  pocket),  54  fig.     SOJ  x  23"".     (U.  S. 
Geological  survey.     Monographs  v.  46.) 

"Bibliography  and  abstract  of  literature"  :  p.  41-124. 


U.  S.  Geological  survey. 

Monographs. 

V.  46.  Bayley,  W.  S.    The  Menominee  iron-bearing  dis- 
trict of  Michigan.      1904. 

U.  S.     Dept.  of  the  Interior. 
see  also 
U.  S.     Geological  survey. 


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